Re: Extract lines from file, add to new files

[dn via Python-list]

On 4/02/24 13:20, avi.e.gr...@gmail.com wrote:

Dave,

You and I have had some experience in teaching or tutoring others and I think 
it fair to say our motivation is closer to teaching someone how they can fish 
for themselves rather than just handing them a fully-cooked fish.


Which may push the debate 'up' a level, in that there are two pertinent 
Python Discussion Lists (amongst the many): Tutor which is expressly for 
learners (and tutors), and this one which is to discuss Python. 
Accordingly, one might suggest that people 'here' are looking for a 
direct answer - the fish (having tried to fish for themselves), but 
learners (seeking to learn to fish) should be asking elsewhere.


This would sort-out the type/level of questions that OPs may have. As 
well as indicating an appropriate approach to 'answers'.


However, there's no rule which says one has to ask in one place or the 
other (nor am I suggesting such, although...). Then again, might the 
lack of forethought evident in some questions and the forum-used, 
indicate a type of person who wouldn't investigate to see which is the 
best place for his/her enquiries anyway?


Tutor List: https://mail.python.org/mailman/listinfo/tutor
Lists Overview: https://mail.python.org/mailman/listinfo



My favorite kinds of questions, thus, include someone who explains what they 
are trying to do and shows some code along with indications of what it produced 
(including error messages) and what it should produce. Then the question should 
not be a request to just FIX THIS or WRITE IT FOR ME but asking if someone can 
show what they did wrong with some idea where it went wrong.

This may not be so common but it allows faster and easier help.


+1


...


I will end with a comment. I have heard of interview techniques for a job where 
they deliberately supply a problem in which the goal is not so much to be easy 
to solve in front of them in real time but to watch how the person looking for 
a job responds to the uncertainties and asks follow-up questions or verbalizes 
things like, if it is like this, I might use this technique but if you also 
need that then ...

So, I shudder to think what happens if someone being interviewed turns around 
and asks us and further confuses things with changes to make it harder to 
recognize they are asking for outside help. The answer expected may well be to 
NOT use say the older versions of PASCAL to do something but switch to 
something better suited (and for that matter available.)  I would not want to 
program the DES encryption/decryption method in Pascal again! And these days, 
it seems much better to just find a module or package that meets such needs.


As you know, I investigate Cognitive Psychology. Accordingly, such is 
interesting to me. In many cases, I'll interview for motivation, not 
just particular skills - but perhaps that's another can-of-worms.


How about "when is 1 + 1 not 2?". This is a bit of a mind-bender, but 
leads towards debugging ability* - what if your code was showing some 
unbelievable result like this?


The answer is (or rather, "could be") 10, ie we're looking at binary cf 
decimal, coding.


Do I hear some groans? Yes, fair-enough! There was absolutely no 
"context" to the question - whereas when coding/debugging we would 
expect to have some 'framing' of our thinking. At the same time, 'fixed 
mode thinking' will prevent many people from even considering such 
possibilities - whether as-asked or in a dev.env...



* In the ?good old days, career progression was thought to be: 
(mainframe) Computer Operator, to Computer Programmer, to Systems 
Analyst, etc. However, as I pointed-out (to an IBM 'big-wig' who took an 
instant dislike as a result) the valued skills of an Analyst are that 
(s)he can see 'patterns' - whereas the skills of debugging involve 
realising why an expected pattern doesn't work (as-expected).



Another analysis might be to decide if the job requires a 'lateral 
thinker' or a more single-minded approach. (us lateral thinkers tend to 
ask (loads of) questions, and thus can be quite 'annoying' individuals).


Then there is the main-stay of many job-adverts: "attention to detail" 
and the question of whether someone who can't [be bothered to] write an 
half-decent email-message (with spell-checker likely built-in) is going 
to be productive when communicating with a pedantic compiler?



Again, some people are suited to this business (or specific jobs 
within), and some (?many) are not - but many are (perhaps reluctantly) 
programming to get some other job done...


--
Regards,
=dn

--
https://mail.python.org/mailman/listinfo/python-list

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Dave,

You and I have had some experience in teaching or tutoring others and I think 
it fair to say our motivation is closer to teaching someone how they can fish 
for themselves rather than just handing them a fully-cooked fish.

My favorite kinds of questions, thus, include someone who explains what they 
are trying to do and shows some code along with indications of what it produced 
(including error messages) and what it should produce. Then the question should 
not be a request to just FIX THIS or WRITE IT FOR ME but asking if someone can 
show what they did wrong with some idea where it went wrong.

This may not be so common but it allows faster and easier help.

But others out there probably can be helped including people who want 
suggestions of approaches to try.

We have discussed some issues here and elsewhere where some purists tend to 
want to stick with close to basic aspects of the language. In some R 
communities, some get upset if someone asks a question (or others supply an 
answer) using non-official add-ons called the tidyverse and I suspect some here 
don't really like discussions that focus mainly on numpy/pandas or so many 
other modules. Yet, the reality is, that except for students who are supposed 
to be learning the basics of the language and show solutions compatible with 
what is being taught in class, others can and should be open to simple 
solutions using non-standard tools that are widely available and vetted. If a 
student is asked to use some method to calculate a value like pi, then 
suggesting they use math.pi is not useful. But if the assignment is to do 
something in trigonometry, it seems a good thing to use as a part of a larger 
solution rather than either embedding a constant to N decimal places or 
calculating it on the f
 ly.

I think people like us who volunteer to reply should consider our choices too. 
I think it is fair to reply, as I saw on the tutor forum, that the code shown 
uses a method that is not the way the replier would do it but nonetheless offer 
some thoughts on particular python coding errors. I am talking about someone 
who wanted to implement a binary tree using a numpy array or something with 
minimal explanation and demanded a fix. They never supplied enough info and I 
think the few who replied backed away. As you mention, they seemed resistant to 
starting over and using data structures that are perhaps more amenable, and in 
any case, the code shown seemed mostly focused on how to make random and 
non-redundant names. 

I will end with a comment. I have heard of interview techniques for a job where 
they deliberately supply a problem in which the goal is not so much to be easy 
to solve in front of them in real time but to watch how the person looking for 
a job responds to the uncertainties and asks follow-up questions or verbalizes 
things like, if it is like this, I might use this technique but if you also 
need that then ...

So, I shudder to think what happens if someone being interviewed turns around 
and asks us and further confuses things with changes to make it harder to 
recognize they are asking for outside help. The answer expected may well be to 
NOT use say the older versions of PASCAL to do something but switch to 
something better suited (and for that matter available.)  I would not want to 
program the DES encryption/decryption method in Pascal again! And these days, 
it seems much better to just find a module or package that meets such needs.

Avi



-Original Message-
From: Python-list  On 
Behalf Of dn via Python-list
Sent: Saturday, February 3, 2024 5:02 PM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

Every trainer, in any field, has to deal with these problems - all the 
time, and over-and-over.


On 4/02/24 06:58, Thomas Passin via Python-list wrote:
> In my view this whole thread became murky and complicated because the OP 
> did not write down the requirements for the program.  Requirements are 
> needed to communicate with other people.  An individual may not need to 
> actually write down the requirements - depending on their complexity - 
> but they always exist even if only vaguely in a person's mind.  The 
> requirements may include what tools or languages the person wants to use 
> and why.
> 
> If you are asking for help, you need to communicate the requirements to 
> the people you are asking for help from.
> 
> The OP may have thought the original post(s) contained enough of the 
> requirements but as we know by now, they didn't.

There is another possible interpretation in such situations (not 
necessarily this one): that the person is fixated on a particular 
solution (and unable/unwilling to adjust his/her thinking to consider 
more widely).

Thus, the question is not: 'here's an entire problem, how can it be 
solved', but more: 'I have a solution, and want help to implement it 
(and only it) just-so'.


The 

Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 2/3/2024 5:02 PM, dn via Python-list wrote:
Every trainer, in any field, has to deal with these problems - all the 
time, and over-and-over.



On 4/02/24 06:58, Thomas Passin via Python-list wrote:
In my view this whole thread became murky and complicated because the 
OP did not write down the requirements for the program.  Requirements 
are needed to communicate with other people.  An individual may not 
need to actually write down the requirements - depending on their 
complexity - but they always exist even if only vaguely in a person's 
mind.  The requirements may include what tools or languages the person 
wants to use and why.


If you are asking for help, you need to communicate the requirements 
to the people you are asking for help from.


The OP may have thought the original post(s) contained enough of the 
requirements but as we know by now, they didn't.


There is another possible interpretation in such situations (not 
necessarily this one): that the person is fixated on a particular 
solution (and unable/unwilling to adjust his/her thinking to consider 
more widely).


Thus, the question is not: 'here's an entire problem, how can it be 
solved', but more: 'I have a solution, and want help to implement it 
(and only it) just-so'.



The latter is an interesting psychology:

1
an experienced person who is trying to translate from one tool to 
another (Python), but discovers that a word-for-word solution is 
difficult because of the artificial-constraints they've placed on the 
situation.


2
a beginner who doesn't know what (s)he doesn't know and comes-up with an 
idea, but fails to appreciate that there is likely more than one path to 
the goal.



The person asking for help may not realize they don't know enough to 
write down all the requirements; an effort to do so may bring that 
lack to visibility.


In the case of 'Beginners' this should probably be taken-as-read!

Which is why we will always find ourselves asking questions or 'please 
give more information'...



However, there are other reasons, eg corporate concerns or personality; 
why people don't want to give more information. The former is reasonable 
(have suffered from same myself). The latter may reveal that the person 
is 'difficult to deal with'...



Mailing lists like these have a drawback that it's hard to impossible 
for someone not involved in a thread to learn anything general from 
it. We can write over and over again to please state clearly what you 
want to do and where the sticking points are, but newcomers post new 
questions without ever reading these pleas.  Then good-hearted people 
who want to be helpful end up spending a lot of time trying to guess 
what is actually being asked for, and maybe never find out with enough 
clarity.  Others take a guess and then spend time working up a 
solution that may or may not be on target.


So please! before posting a request for help, write down the 
requirements as best you can figure them out, and then make sure that 
they are expressed such that the readers can understand.


Unfortunately, if the person doesn't understand the problem (leave-aside 
any ideas of solution), then (s)he will not be able to clearly 
communicate same to us, in any way, shape, or form...


Which brings one to the question: if a person cannot express the problem 
clearly and completely, is (s)he suited to development work? If the 
problem is not understood, could 'the solution' ever be more than an 
exercise in hope?

(prototyping and experimentation aside)


Pairs programming can be fun and productive, if you are lucky to have 
the right person to work with.  I've had one person like that over the 
years.


Yes, it is frustrating to invest time and effort in helping someone, 
only for same to disappear 'into a black hole'. The lack of response 
seems to indicate a lack of respect or appreciation. Is this perhaps 
part of today's "consumer" life-style, where so few are contributors or 
creators?



On the other side of that coin: do the people who make assumptions and 
(kindly) blaze-ahead with 'a solution', actually help the conversation? 
If the assumptions are correct, yes! What if they are not?



...and don't get me started on folk who want us to do their 
training-assignments or build some application, for them!



As a slight aside: on one training-course DiscussionList/BulletinBoard 
set-up, if a trainee asked a question without a descriptive 
title/SubjectLine, eg "Python not working" or "Urgent: please help"; I 
asked them to re-post with a title that would help others in a similar 
situation find the topic - and closed the original thread.


Some found it "brutal" - probably skewing towards those who felt 
"Urgent" because they'd left things too close to deadline. Others joined 
the (later) thread because they could identify the topic and realise 
their interest in learning or contributing to the conversation...



Time pressures lead to a multitude of evils!


There's a 

Re: Extract lines from file, add to new files

[dn via Python-list]

Every trainer, in any field, has to deal with these problems - all the 
time, and over-and-over.



On 4/02/24 06:58, Thomas Passin via Python-list wrote:
In my view this whole thread became murky and complicated because the OP 
did not write down the requirements for the program.  Requirements are 
needed to communicate with other people.  An individual may not need to 
actually write down the requirements - depending on their complexity - 
but they always exist even if only vaguely in a person's mind.  The 
requirements may include what tools or languages the person wants to use 
and why.


If you are asking for help, you need to communicate the requirements to 
the people you are asking for help from.


The OP may have thought the original post(s) contained enough of the 
requirements but as we know by now, they didn't.


There is another possible interpretation in such situations (not 
necessarily this one): that the person is fixated on a particular 
solution (and unable/unwilling to adjust his/her thinking to consider 
more widely).


Thus, the question is not: 'here's an entire problem, how can it be 
solved', but more: 'I have a solution, and want help to implement it 
(and only it) just-so'.



The latter is an interesting psychology:

1
an experienced person who is trying to translate from one tool to 
another (Python), but discovers that a word-for-word solution is 
difficult because of the artificial-constraints they've placed on the 
situation.


2
a beginner who doesn't know what (s)he doesn't know and comes-up with an 
idea, but fails to appreciate that there is likely more than one path to 
the goal.



The person asking for help may not realize they don't know enough to 
write down all the requirements; an effort to do so may bring that lack 
to visibility.


In the case of 'Beginners' this should probably be taken-as-read!

Which is why we will always find ourselves asking questions or 'please 
give more information'...



However, there are other reasons, eg corporate concerns or personality; 
why people don't want to give more information. The former is reasonable 
(have suffered from same myself). The latter may reveal that the person 
is 'difficult to deal with'...



Mailing lists like these have a drawback that it's hard to impossible 
for someone not involved in a thread to learn anything general from it. 
We can write over and over again to please state clearly what you want 
to do and where the sticking points are, but newcomers post new 
questions without ever reading these pleas.  Then good-hearted people 
who want to be helpful end up spending a lot of time trying to guess 
what is actually being asked for, and maybe never find out with enough 
clarity.  Others take a guess and then spend time working up a solution 
that may or may not be on target.


So please! before posting a request for help, write down the 
requirements as best you can figure them out, and then make sure that 
they are expressed such that the readers can understand.


Unfortunately, if the person doesn't understand the problem (leave-aside 
any ideas of solution), then (s)he will not be able to clearly 
communicate same to us, in any way, shape, or form...


Which brings one to the question: if a person cannot express the problem 
clearly and completely, is (s)he suited to development work? If the 
problem is not understood, could 'the solution' ever be more than an 
exercise in hope?

(prototyping and experimentation aside)


Yes, it is frustrating to invest time and effort in helping someone, 
only for same to disappear 'into a black hole'. The lack of response 
seems to indicate a lack of respect or appreciation. Is this perhaps 
part of today's "consumer" life-style, where so few are contributors or 
creators?



On the other side of that coin: do the people who make assumptions and 
(kindly) blaze-ahead with 'a solution', actually help the conversation? 
If the assumptions are correct, yes! What if they are not?



...and don't get me started on folk who want us to do their 
training-assignments or build some application, for them!



As a slight aside: on one training-course DiscussionList/BulletinBoard 
set-up, if a trainee asked a question without a descriptive 
title/SubjectLine, eg "Python not working" or "Urgent: please help"; I 
asked them to re-post with a title that would help others in a similar 
situation find the topic - and closed the original thread.


Some found it "brutal" - probably skewing towards those who felt 
"Urgent" because they'd left things too close to deadline. Others joined 
the (later) thread because they could identify the topic and realise 
their interest in learning or contributing to the conversation...



Time pressures lead to a multitude of evils!


There's a quotation that goes something like "the poor will be with your 
always"?

(?possibly Biblical)

Whether we (here) are talking about 'poor' manners, 'poor' 
understanding, 'poor' communication skills, 'poor' 

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

We substantially agree with that, Thomas.  In the best of all possible
worlds, someone who gets stuck will sit down and try to carefully spell out
things in ways like you mention and, incidentally, may often catch the error
or figure out how to do it and not even send in a request! LOL!

I think a main thing that the OP and others can do is to not just be
abstract but supply a small example including what output they expect and
perhaps what they did not receive properly along with error messages.

Rich had not tried doing what he wanted in python, yet. I don't know if he
did any other parts yet. I think he was still in a somewhat abstract design
state and hoping for someone to push him at something like a resource to
continue and he did accept suggestions on what now seem somewhat random
things to read as people guessed.

In a sense, I and others can take some blame for the way we widened the
problem while trying to look at it our own way.

But looking back, I think Rich asked close to what he wanted. An example
might have helped such as:

'I have information about multiple clients including an email address and a
human name such as:

u...@domain.com Sally
f...@bark.com Barky

I want to save the info in a file or maybe two in such a way that when I
write a program and ask it to send an email to "f...@bark.com" then it finds
an entry that matches the email address and then uses that to find the
matching name and sends a specified message with a specific salutation in
front like "Dear Barky,".

I was thinking of having two files with one having email address after
another and the other having the corresponding names. I want to use python
to search one file and then return the name in the other. Are there other
and perhaps better ways commonly used to associate one keyword with a
value?'

Back to me. The above is not polished but might still have engendered a
discussion such as how to keep the files synchronized. Yes, the OP could
have added endless clauses saying that they are not asking how to create the
data files or keep them synchronized but just how to match them. The reply
in this case possibly could have suggested they count the lines they have
read until the match and, assuming no blank lines are used, read a second
file till the nth line. We might have been done quickly and THEN had a long
discussion about other ways!

I have participated, like you, in another forum designed for tutoring and I
think the rules and expectations there may be a bit different. Over here, it
is fairer to expect people to take a bit of time and ask clearer questions. 

We live and we learn and then Alzheimer's ...



-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Saturday, February 3, 2024 12:59 PM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

In my view this whole thread became murky and complicated because the OP 
did not write down the requirements for the program.  Requirements are 
needed to communicate with other people.  An individual may not need to 
actually write down the requirements - depending on their complexity - 
but they always exist even if only vaguely in a person's mind.  The 
requirements may include what tools or languages the person wants to use 
and why.

If you are asking for help, you need to communicate the requirements to 
the people you are asking for help from.

The OP may have thought the original post(s) contained enough of the 
requirements but as we know by now, they didn't.

The person asking for help may not realize they don't know enough to 
write down all the requirements; an effort to do so may bring that lack 
to visibility.

Mailing lists like these have a drawback that it's hard to impossible 
for someone not involved in a thread to learn anything general from it. 
We can write over and over again to please state clearly what you want 
to do and where the sticking points are, but newcomers post new 
questions without ever reading these pleas.  Then good-hearted people 
who want to be helpful end up spending a lot of time trying to guess 
what is actually being asked for, and maybe never find out with enough 
clarity.  Others take a guess and then spend time working up a solution 
that may or may not be on target.

So please! before posting a request for help, write down the 
requirements as best you can figure them out, and then make sure that 
they are expressed such that the readers can understand.

On 2/3/2024 11:33 AM, avi.e.gr...@gmail.com wrote:
> Thomas,
> 
> I have been thinking about the concept of being stingy with information as
> this is a fairly common occurrence when people ask for help. They often
ask
> for what they think they want while people like us keep asking why they
want
> that and perhaps offer guidance on how to get closer to what they NEED or
a
> better way.
> 
> In retrospect, Rich did give all the info he thought he n

Re: Extract lines from file, add to new files

[Mats Wichmann via Python-list]

On 2/3/24 10:58, Thomas Passin via Python-list wrote:
In my view this whole thread became murky and complicated because the OP 
did not write down the requirements for the program.  Requirements are 
needed to communicate with other people.  An individual may not need to 
actually write down the requirements - depending on their complexity - 
but they always exist even if only vaguely in a person's mind.  The 
requirements may include what tools or languages the person wants to use 
and why.


If you are asking for help, you need to communicate the requirements to 
the people you are asking for help from.


The OP may have thought the original post(s) contained enough of the 
requirements but as we know by now, they didn't.


The person asking for help may not realize they don't know enough to 
write down all the requirements; an effort to do so may bring that lack 
to visibility.


Mailing lists like these have a drawback that it's hard to impossible 
for someone not involved in a thread to learn anything general from it. 
We can write over and over again to please state clearly what you want 
to do and where the sticking points are, but newcomers post new 
questions without ever reading these pleas.  Then good-hearted people 
who want to be helpful end up spending a lot of time trying to guess 
what is actually being asked for, and maybe never find out with enough 
clarity.  Others take a guess and then spend time working up a solution 
that may or may not be on target.


So please! before posting a request for help, write down the 
requirements as best you can figure them out, and then make sure that 
they are expressed such that the readers can understand.


Indeed.  I've occasionally practised the following technique (in some 
form) over the years without knowing it had grown a name, and wikipedia 
page to go with it.  It may be handy to use to help come up with a 
clearer explanation before sending off a post to a mailing list or other 
static medium, because of the inevitable delays in going back and forth. 
Interactive formus like the Python Discord have a bit of an advantage in 
that you can try to tease out the intent more quickly.  But as you 
say... a newcomer won't know this.


https://en.wikipedia.org/wiki/Rubber_duck_debugging

--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

In my view this whole thread became murky and complicated because the OP 
did not write down the requirements for the program.  Requirements are 
needed to communicate with other people.  An individual may not need to 
actually write down the requirements - depending on their complexity - 
but they always exist even if only vaguely in a person's mind.  The 
requirements may include what tools or languages the person wants to use 
and why.


If you are asking for help, you need to communicate the requirements to 
the people you are asking for help from.


The OP may have thought the original post(s) contained enough of the 
requirements but as we know by now, they didn't.


The person asking for help may not realize they don't know enough to 
write down all the requirements; an effort to do so may bring that lack 
to visibility.


Mailing lists like these have a drawback that it's hard to impossible 
for someone not involved in a thread to learn anything general from it. 
We can write over and over again to please state clearly what you want 
to do and where the sticking points are, but newcomers post new 
questions without ever reading these pleas.  Then good-hearted people 
who want to be helpful end up spending a lot of time trying to guess 
what is actually being asked for, and maybe never find out with enough 
clarity.  Others take a guess and then spend time working up a solution 
that may or may not be on target.


So please! before posting a request for help, write down the 
requirements as best you can figure them out, and then make sure that 
they are expressed such that the readers can understand.


On 2/3/2024 11:33 AM, avi.e.gr...@gmail.com wrote:

Thomas,

I have been thinking about the concept of being stingy with information as
this is a fairly common occurrence when people ask for help. They often ask
for what they think they want while people like us keep asking why they want
that and perhaps offer guidance on how to get closer to what they NEED or a
better way.

In retrospect, Rich did give all the info he thought he needed. It boiled
down to saying that he wants to distribute data into two files in such a way
that finding an item in file A then lets him find the corresponding item in
file B. He was not worried about how to make the files or what to do with
the info afterward. He had those covered and was missing what he considered
a central piece. And, it seems he programs in multiple languages and
environments as needed and is not exactly a newbie. He just wanted a way to
implement his overall design.

We threw many solutions and ideas at him but some of us (like me) also got
frustrated as some ideas were not received due to one objection or another
that had not been mentioned earlier when it was not seen as important.

I particularly notice a disconnect some of us had. Was this supposed to be a
search that read only as much as needed to find something and stopped
reading, or a sort of filter that returned zero or more matches and went to
the end, or perhaps something that read entire files and swallowed them into
data structures in memory and then searched and found corresponding entries,
or maybe something else?

All the above approaches could work but some designs not so much. For
example, some files are too large. We, as programmers, often consciously or
unconsciously look at many factors to try to zoom in on what approaches me
might use. To be given minimal amounts of info can be frustrating. We worry
about making a silly design. But the OP may want something minimal and not
worry as long as it is fairly easy to program and works.

We could have suggested something very simple like:

Open both files A and B
In a loop get a line from each. If the line from A is a match, do something
with the current line from B.
If you are getting only one, exit the loop.

Or, if willing, we could have suggested any other file format, such as a
CSV, in which the algorithm is similar but different as in:

Open file A
Read a line in a loop
Split it in parts
If the party of the first part matches something, use the party of the
second part

Or, of course, suggest they read the entire file, into a list of lines or a
data.frame and use some tools that search all of it and produce results.

I find I personally now often lean toward the latter approach but ages ago
when memory and CPU were considerations and maybe garbage collection was not
automatic, ...


-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Wednesday, January 31, 2024 7:25 AM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 1/30/2024 11:25 PM, avi.e.gr...@gmail.com wrote:

Thomas, on some points we may see it differently.


I'm mostly going by what the OP originally asked for back on Jan 11.
He's been too stingy with information since then to be worth spending
much time on, IMHO.


Some formats can be done simply but are maybe better done in somewhat
standard

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Thomas,

I have been thinking about the concept of being stingy with information as
this is a fairly common occurrence when people ask for help. They often ask
for what they think they want while people like us keep asking why they want
that and perhaps offer guidance on how to get closer to what they NEED or a
better way.

In retrospect, Rich did give all the info he thought he needed. It boiled
down to saying that he wants to distribute data into two files in such a way
that finding an item in file A then lets him find the corresponding item in
file B. He was not worried about how to make the files or what to do with
the info afterward. He had those covered and was missing what he considered
a central piece. And, it seems he programs in multiple languages and
environments as needed and is not exactly a newbie. He just wanted a way to
implement his overall design.

We threw many solutions and ideas at him but some of us (like me) also got
frustrated as some ideas were not received due to one objection or another
that had not been mentioned earlier when it was not seen as important.

I particularly notice a disconnect some of us had. Was this supposed to be a
search that read only as much as needed to find something and stopped
reading, or a sort of filter that returned zero or more matches and went to
the end, or perhaps something that read entire files and swallowed them into
data structures in memory and then searched and found corresponding entries,
or maybe something else?

All the above approaches could work but some designs not so much. For
example, some files are too large. We, as programmers, often consciously or
unconsciously look at many factors to try to zoom in on what approaches me
might use. To be given minimal amounts of info can be frustrating. We worry
about making a silly design. But the OP may want something minimal and not
worry as long as it is fairly easy to program and works.

We could have suggested something very simple like:

Open both files A and B
In a loop get a line from each. If the line from A is a match, do something
with the current line from B.
If you are getting only one, exit the loop.

Or, if willing, we could have suggested any other file format, such as a
CSV, in which the algorithm is similar but different as in:

Open file A
Read a line in a loop
Split it in parts
If the party of the first part matches something, use the party of the
second part

Or, of course, suggest they read the entire file, into a list of lines or a
data.frame and use some tools that search all of it and produce results.

I find I personally now often lean toward the latter approach but ages ago
when memory and CPU were considerations and maybe garbage collection was not
automatic, ...


-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Wednesday, January 31, 2024 7:25 AM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 1/30/2024 11:25 PM, avi.e.gr...@gmail.com wrote:
> Thomas, on some points we may see it differently.

I'm mostly going by what the OP originally asked for back on Jan 11. 
He's been too stingy with information since then to be worth spending 
much time on, IMHO.

> Some formats can be done simply but are maybe better done in somewhat
> standard ways.
> 
> Some of what the OP has is already tables in a database and that can
> trivially be exported into a CSV file or other formats like your TSV file
> and more. They can also import from there. As I mentioned, many
spreadsheets
> and all kinds of statistical programs tend to support some formats making
it
> quite flexible.
> 
> Python has all kinds of functionality, such as in the pandas module, to
read
> in a CSV or write it out. And once you have the data structure in memory,
al
> kinds of queries and changes can be made fairly straightforwardly. As one
> example, Rich has mentioned wanting finer control in selecting who gets
some
> version of the email based on concepts like market segmentation. He
already
> may have info like the STATE (as in Arizona) in his database. He might at
> some point enlarge his schema so each entry is placed in one or more
> categories and thus his CSV, once imported, can do the usual tasks of
> selecting various rows and columns or doing joins or whatever.
> 
> Mind you, another architecture could place quite a bit of work completely
on
> the back end and he could send SQL queries to the database from python and
> get back his results into python which would then make the email messages
> and pass them on to other functionality to deliver. This would remove any
> need for files and just rely on the DB.
> 
> There as as usual, too many choices and not necessarily one best answer.
Of
> course if this was a major product that would be heavily used, sure, you
> could tweak and optimize. As it is, Rich is getting a chance to im

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

This discussion has circled back to where it started. It illustrates quite a
few points about how many different ways someone can do something as well as
doing it using different tools and also about how others may see aspects of
mission creep as they look for making it perfect when it need not be. I mean
the OP wants a simple personal tool and is not currently concerned with lots
of things.

The data seems to be in a data base and can be extracted from there into one
or two files mostly for convenience. Presumably, all the usual
additions/deletions/modifications are being done in the DB. If so, then as
long as his latest vision of having two synchronized files is done
consistently by making both, they are in sync.

In addition, it sounds like the original idea was a tad too simple. The OP
wanted to add a single-line or so at the head of a message that simply
interpolates a name. This could be handled with all kinds of
form-letter-merge methods as well as search and replace methods of great
generality. But, for now, the OP is asking for something truly simple and
would be happy with a solution that is slow and clunky and uses a few
utilities in a shell script on LINUX. I took a look at doing this on bash
and ran into some surprises as this would have been trivial for me in a
shell like ksh. Setting variables is now done in a subshell which was done
why? All I know is if you could simply read a file one line at a time in a
loop and set one or more variables, then it becomes easy to use something
like combining an echo and a cat of the original message to make a message
with a variable heading and feed that to the mailer. And if the storage
format was CSV, again, you could easily peel it apart using something like
cut or awk or whatever.

The main reason for trying it in python may have been frustration with doing
it as a shell script. Fair enough. But the idea of two files may have been
made in the first place by the original idea of such a script. The question
posed was sort of how to search in one and then somehow find the
corresponding part of another. The mindset of the OP may have been focused
in a direction we were not clear on. As an example, there are ways to search
file A and get back a line number of the first match and then using perhaps
another utility you ask it to scan file B and just print out that line
number and nothing else.

The current solution the OP is considering sounds like a loop that goes
through both files in parallel. This would mean when one loop finds what it
is looking for, the other delivers what is in the same location. That may
work well enough for the purpose.

But I have learned over the years that having a few well-designed tools and
ideas and using them consistently, is often a good way to get results even
if it is not as imaginative and efficient as some other. If you are allowed
to design something from top to bottom, there may be very nice solutions.
But if asked to just do one small part in a design that already feels it has
solved other aspects, then suggesting they start over is often not taken
well. LOL!

I happen to think some storage format such as CSV would be a good idea IFF
doing this in Python for some reasons I mentioned earlier. I am not in love
with CSV and use other data formats as needed and some others would be fine
as long as your toolkit included some easy and reliable way to read the
contents in and manipulate to get your results. I do programming in multiple
languages and whether I am using python or something like R, I often end up
importing the data into some data.frame format, performing a pipeline of
manipulations using it and perhaps other such structures and generating
results and optionally saving some back to files. Tons of well-tested and
comfortable tools can be used if the data is set up right so even when it
can be easily done by hand, it may not be worth the effort as the standard
tools and tricks work and work fast enough.

Rich (AKA the OP) seems satisfied with having a solution. It may not be
ideal but for his needs, ...


-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Wednesday, January 31, 2024 10:36 AM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 1/31/2024 9:05 AM, Rich Shepard via Python-list wrote:
> On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:
> 
>> If I had a script that's been working for 30 years, I'd probably just use
>> Python to do the personalizing and let the rest of the bash script do the
>> rest, like it always has. The Python program would pipe or send the
>> personalized messages to the rest of the bash program. Something in that
>> ballpark, anyway.
> 
> Thomas,
> 
> A bash shell script looks easier for me and more promising. Using a while
> loop (one for the name file the other for the address file), and sed for
> putting the name at the head of the

Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/31/2024 9:05 AM, Rich Shepard via Python-list wrote:

On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:


If I had a script that's been working for 30 years, I'd probably just use
Python to do the personalizing and let the rest of the bash script do the
rest, like it always has. The Python program would pipe or send the
personalized messages to the rest of the bash program. Something in that
ballpark, anyway.


Thomas,

A bash shell script looks easier for me and more promising. Using a while
loop (one for the name file the other for the address file), and sed for
putting the name at the head of the message replacing a generic placeholder
should work with the existing for loop script.


Sounds good.  I'd still be a bit worried about the two files getting out 
of sync, as others have mentioned.


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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:


If I had a script that's been working for 30 years, I'd probably just use
Python to do the personalizing and let the rest of the bash script do the
rest, like it always has. The Python program would pipe or send the
personalized messages to the rest of the bash program. Something in that
ballpark, anyway.


Thomas,

A bash shell script looks easier for me and more promising. Using a while
loop (one for the name file the other for the address file), and sed for
putting the name at the head of the message replacing a generic placeholder
should work with the existing for loop script.

Thanks,

Rich
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Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/30/2024 11:25 PM, avi.e.gr...@gmail.com wrote:

Thomas, on some points we may see it differently.


I'm mostly going by what the OP originally asked for back on Jan 11. 
He's been too stingy with information since then to be worth spending 
much time on, IMHO.



Some formats can be done simply but are maybe better done in somewhat
standard ways.

Some of what the OP has is already tables in a database and that can
trivially be exported into a CSV file or other formats like your TSV file
and more. They can also import from there. As I mentioned, many spreadsheets
and all kinds of statistical programs tend to support some formats making it
quite flexible.

Python has all kinds of functionality, such as in the pandas module, to read
in a CSV or write it out. And once you have the data structure in memory, al
kinds of queries and changes can be made fairly straightforwardly. As one
example, Rich has mentioned wanting finer control in selecting who gets some
version of the email based on concepts like market segmentation. He already
may have info like the STATE (as in Arizona) in his database. He might at
some point enlarge his schema so each entry is placed in one or more
categories and thus his CSV, once imported, can do the usual tasks of
selecting various rows and columns or doing joins or whatever.

Mind you, another architecture could place quite a bit of work completely on
the back end and he could send SQL queries to the database from python and
get back his results into python which would then make the email messages
and pass them on to other functionality to deliver. This would remove any
need for files and just rely on the DB.

There as as usual, too many choices and not necessarily one best answer. Of
course if this was a major product that would be heavily used, sure, you
could tweak and optimize. As it is, Rich is getting a chance to improve his
python skills no matter which way he goes.



-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Tuesday, January 30, 2024 10:37 PM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 1/30/2024 12:21 PM, Rich Shepard via Python-list wrote:

On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:


Fine, my toy example will still be applicable. But, you know, you haven't
told us enough to give you help. Do you want to replace text from values
in a file? That's been covered. Do you want to send the messages using
those libraries? You haven't said what you don't know how to do.
Something
else? What is it that you want to do that you don't know how?


Thomas,

For 30 years I've used a bash script using mailx to send messages to a

list

of recipients. They have no salutation to personalize each one. Since I
want
to add that personalized salutation I decided to write a python script to
replace the bash script.

I have collected 11 docs explaining the smtplib and email modules and
providing example scripts to apply them to send multiple individual
messages
with salutations and attachments.


If I had a script that's been working for 30 years, I'd probably just
use Python to do the personalizing and let the rest of the bash script
do the rest, like it always has.  The Python program would pipe or send
the personalized messages to the rest of the bash program. Something in
that ballpark, anyway.


Today I'm going to be reading these. They each recommend using .csv input
files for names and addresses. My first search is learning whether I can
write a single .csv file such as:
"name1","address1"
"mane2","address2"
which I believe will work; and by inserting at the top of the message

block

Hi, {yourname}
the name in the .csv file will replace the bracketed place holder

If the file contents are going to be people's names and email addresses,
I would just tab separate them and split each line on the tab.  Names
aren't going to include tabs so that would be safe.  Email addresses
might theoretically include a tab inside a quoted name but that would be
extremely obscure and unlikely.  No need for CSV, it would just add
complexity.

data = f.readlines()
for d in data:
  name, addr = line.split('\t') if line.strip() else ('', '')


Still much to learn and the batch of downloaded PDF files should educate
me.

Regards,

Rich




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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Thomas, on some points we may see it differently.

Some formats can be done simply but are maybe better done in somewhat
standard ways.

Some of what the OP has is already tables in a database and that can
trivially be exported into a CSV file or other formats like your TSV file
and more. They can also import from there. As I mentioned, many spreadsheets
and all kinds of statistical programs tend to support some formats making it
quite flexible.

Python has all kinds of functionality, such as in the pandas module, to read
in a CSV or write it out. And once you have the data structure in memory, al
kinds of queries and changes can be made fairly straightforwardly. As one
example, Rich has mentioned wanting finer control in selecting who gets some
version of the email based on concepts like market segmentation. He already
may have info like the STATE (as in Arizona) in his database. He might at
some point enlarge his schema so each entry is placed in one or more
categories and thus his CSV, once imported, can do the usual tasks of
selecting various rows and columns or doing joins or whatever.

Mind you, another architecture could place quite a bit of work completely on
the back end and he could send SQL queries to the database from python and
get back his results into python which would then make the email messages
and pass them on to other functionality to deliver. This would remove any
need for files and just rely on the DB.

There as as usual, too many choices and not necessarily one best answer. Of
course if this was a major product that would be heavily used, sure, you
could tweak and optimize. As it is, Rich is getting a chance to improve his
python skills no matter which way he goes.



-Original Message-
From: Python-list  On
Behalf Of Thomas Passin via Python-list
Sent: Tuesday, January 30, 2024 10:37 PM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 1/30/2024 12:21 PM, Rich Shepard via Python-list wrote:
> On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:
> 
>> Fine, my toy example will still be applicable. But, you know, you haven't
>> told us enough to give you help. Do you want to replace text from values
>> in a file? That's been covered. Do you want to send the messages using
>> those libraries? You haven't said what you don't know how to do. 
>> Something
>> else? What is it that you want to do that you don't know how?
> 
> Thomas,
> 
> For 30 years I've used a bash script using mailx to send messages to a
list
> of recipients. They have no salutation to personalize each one. Since I 
> want
> to add that personalized salutation I decided to write a python script to
> replace the bash script.
> 
> I have collected 11 docs explaining the smtplib and email modules and
> providing example scripts to apply them to send multiple individual 
> messages
> with salutations and attachments.

If I had a script that's been working for 30 years, I'd probably just 
use Python to do the personalizing and let the rest of the bash script 
do the rest, like it always has.  The Python program would pipe or send 
the personalized messages to the rest of the bash program. Something in 
that ballpark, anyway.

> Today I'm going to be reading these. They each recommend using .csv input
> files for names and addresses. My first search is learning whether I can
> write a single .csv file such as:
> "name1","address1"
> "mane2","address2"
> which I believe will work; and by inserting at the top of the message
block
> Hi, {yourname}
> the name in the .csv file will replace the bracketed place holder
If the file contents are going to be people's names and email addresses, 
I would just tab separate them and split each line on the tab.  Names 
aren't going to include tabs so that would be safe.  Email addresses 
might theoretically include a tab inside a quoted name but that would be 
extremely obscure and unlikely.  No need for CSV, it would just add 
complexity.

data = f.readlines()
for d in data:
 name, addr = line.split('\t') if line.strip() else ('', '')

> Still much to learn and the batch of downloaded PDF files should educate 
> me.
> 
> Regards,
> 
> Rich

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Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/30/2024 12:21 PM, Rich Shepard via Python-list wrote:

On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:


Fine, my toy example will still be applicable. But, you know, you haven't
told us enough to give you help. Do you want to replace text from values
in a file? That's been covered. Do you want to send the messages using
those libraries? You haven't said what you don't know how to do. 
Something

else? What is it that you want to do that you don't know how?


Thomas,

For 30 years I've used a bash script using mailx to send messages to a list
of recipients. They have no salutation to personalize each one. Since I 
want

to add that personalized salutation I decided to write a python script to
replace the bash script.

I have collected 11 docs explaining the smtplib and email modules and
providing example scripts to apply them to send multiple individual 
messages

with salutations and attachments.


If I had a script that's been working for 30 years, I'd probably just 
use Python to do the personalizing and let the rest of the bash script 
do the rest, like it always has.  The Python program would pipe or send 
the personalized messages to the rest of the bash program. Something in 
that ballpark, anyway.



Today I'm going to be reading these. They each recommend using .csv input
files for names and addresses. My first search is learning whether I can
write a single .csv file such as:
"name1","address1"
"mane2","address2"
which I believe will work; and by inserting at the top of the message block
Hi, {yourname}
the name in the .csv file will replace the bracketed place holder
If the file contents are going to be people's names and email addresses, 
I would just tab separate them and split each line on the tab.  Names 
aren't going to include tabs so that would be safe.  Email addresses 
might theoretically include a tab inside a quoted name but that would be 
extremely obscure and unlikely.  No need for CSV, it would just add 
complexity.


data = f.readlines()
for d in data:
name, addr = line.split('\t') if line.strip() else ('', '')

Still much to learn and the batch of downloaded PDF files should educate 
me.


Regards,

Rich


--
https://mail.python.org/mailman/listinfo/python-list

Re: Aw: Re: Extract lines from file, add to new files

[Mats Wichmann via Python-list]

On 1/30/24 14:46, AVI GROSS via Python-list wrote:

Rich,

You may want to broaden your perspective a bit when people make suggestions.

Karsten did not spell out a full design and should not need to.

But consider this as a scenario.

You want to send (almost) the same message to one or more recipients.

So call a program, perhaps some variant on a shell script, that does some
prep work such as maybe creating a temporary or working directory/folder.
Had one copy of your message ready in a file somewhere, Have a way to get a
list of recipients intended and the file or files containing enough info to
link email addresses to human names and anything else such as their
preferred pronoun  or address.


I'd say based on the bits of the problem description I *have* absorbed, 
which almost certainly isn't all of them, there's a fairly basic 
capability, not terribly often used in my experience, that might be of 
some use:


https://docs.python.org/3/library/string.html#template-strings


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RE: Aw: Re: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Rich,

You may want to broaden your perspective a bit when people make suggestions.

Karsten did not spell out a full design and should not need to.

But consider this as a scenario.

You want to send (almost) the same message to one or more recipients.

So call a program, perhaps some variant on a shell script, that does some
prep work such as maybe creating a temporary or working directory/folder.
Had one copy of your message ready in a file somewhere, Have a way to get a
list of recipients intended and the file or files containing enough info to
link email addresses to human names and anything else such as their
preferred pronoun  or address.

Now have the script call your super-duper python program with enough info so
it can find the folder to put amended COPIES of your letter into as well as.
Perhaps the email address intended in the filename or whatever works for
you. 

Your program will then simply identify each email recipient you want and
look up the other info and prepend the customized salutation, or make
substitutions in the template and write out a new file in the designated
folder with perhaps the email address as the filename.

When your loop ends, exit the python program with success, or perhaps report
some failure.

The shell script now resumes by checking the exit status and if OK,
continuing to enter the folder and loop on all file contests and invoke the
functionality to send each copied/enhanced file to the intended recipient.
If you also need to support attachments, you can figure out how to attach
the same ones to each as I assume those are not changed for each recipient. 

It may keep track of how many worked or failed and eventually clear out the
files and perhaps the folder and you are done.

This is NOT a required way to do it but for what sounds like a limited
personal project, it should work well enough and have you do the limited
amount of work you need in Python.

Having said that, you can likely also easily do everything without python
and I have written some huge shell scripts in my time to do way more complex
things. But learning how to do things like this well in python can be time
well spent as long as you don't tackle too much at a time and get
overwhelmed.




-Original Message-
From: Python-list  On
Behalf Of Rich Shepard via Python-list
Sent: Tuesday, January 30, 2024 12:53 PM
To: python-list@python.org
Subject: Re: Aw: Re: Extract lines from file, add to new files

On Tue, 30 Jan 2024, Karsten Hilbert wrote:

> Why not foxus on just the part you think you are better off using python,
> namely personalization ?
>
> Create personalized files and send them with your trusted mailx solution ?

Karsten,

Too much time. And while mailx accepts the '-a' option for attachments but
has none for individual salutations.

Regards,

Rich
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Aw: Re: Re: Re: Extract lines from file, add to new files

[Karsten Hilbert via Python-list]

> On Tue, 30 Jan 2024, Karsten Hilbert wrote:
>
> > It doesn't need to. It just sends the (pre-personalized-by-Python) mail 
> > files.
>
> Karsten,
>
> In which case, I might as well have Python format and send the messages. :-)

Certainly. But it seems you are wrestling with Python. Might as well reduce the 
attack surface.

Karsten
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Re: Aw: Re: Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Tue, 30 Jan 2024, Karsten Hilbert wrote:


It doesn't need to. It just sends the (pre-personalized-by-Python) mail files.


Karsten,

In which case, I might as well have Python format and send the messages. :-)

Regards,

Rich
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Aw: Re: Re: Extract lines from file, add to new files

[Karsten Hilbert via Python-list]

> > Why not foxus on just the part you think you are better off using python,
> > namely personalization ?
> >
> > Create personalized files and send them with your trusted mailx solution ?
>
> Karsten,
>
> Too much time. And while mailx accepts the '-a' option for attachments but
> has none for individual salutations.

It doesn't need to. It just sends the (pre-personalized-by-Python) mail files.

Karsten
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Re: Aw: Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Tue, 30 Jan 2024, Karsten Hilbert wrote:


Why not foxus on just the part you think you are better off using python,
namely personalization ?

Create personalized files and send them with your trusted mailx solution ?


Karsten,

Too much time. And while mailx accepts the '-a' option for attachments but
has none for individual salutations.

Regards,

Rich
--
https://mail.python.org/mailman/listinfo/python-list

Aw: Re: Extract lines from file, add to new files

[Karsten Hilbert via Python-list]

> For 30 years I've used a bash script using mailx to send messages to a list
> of recipients. They have no salutation to personalize each one. Since I want
> to add that personalized salutation I decided to write a python script to
> replace the bash script.

Why not foxus on just the part you think you are better off using python, namely
personalization ?

Create personalized files and send them with your trusted mailx solution ?

That'll take out wrestling with smptlib et al.

Karsten

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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Tue, 30 Jan 2024, AVI GROSS via Python-list wrote:


But seriously, the OP, AKA Rich, is making clear that he is making a tool
for his own use. It sounds like he wants to maintain a data repository of
his own with some info about his clients and then have the ability to
specify a name and pop up an email directed to them, or something along
those lines.


Close, Avi.

I have no issues sending messages to single individuals or mailing lists. I
want to send the same message to several individuals at one time, which I've
done -- without individual salutations -- for 30 years using a bash script
and mailx.

As I replied to Thomas on the list, I've downloaded 11 PDF docs from the Web
(and a useful book on the Python3 standard library) and will start reading
and learning from them today. I expect to find answers to my few remaining
questions in these docs.

Regards,

Rich
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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Tue, 30 Jan 2024, Thomas Passin via Python-list wrote:


Fine, my toy example will still be applicable. But, you know, you haven't
told us enough to give you help. Do you want to replace text from values
in a file? That's been covered. Do you want to send the messages using
those libraries? You haven't said what you don't know how to do. Something
else? What is it that you want to do that you don't know how?


Thomas,

For 30 years I've used a bash script using mailx to send messages to a list
of recipients. They have no salutation to personalize each one. Since I want
to add that personalized salutation I decided to write a python script to
replace the bash script.

I have collected 11 docs explaining the smtplib and email modules and
providing example scripts to apply them to send multiple individual messages
with salutations and attachments.

Today I'm going to be reading these. They each recommend using .csv input
files for names and addresses. My first search is learning whether I can
write a single .csv file such as:
"name1","address1"
"mane2","address2"
which I believe will work; and by inserting at the top of the message block
Hi, {yourname}
the name in the .csv file will replace the bracketed place holder.

Still much to learn and the batch of downloaded PDF files should educate me.

Regards,

Rich
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

I deleted the contents of the message so I can avoid both of  the deadly
sins of top posting and bottom posting and chance committing  the sin of
replying without any context.

Of course, I am only replying to Jon wishing a real or feigned good luck to
the OP.

But seriously, the OP, AKA Rich, is making clear that he is making a tool
for his own use. It sounds like he wants to maintain a data repository of
his own with some info about his clients and then have the ability to
specify a name and pop up an email directed to them, or something along
those lines.

Without further info, this sounds like what quite a few popular and even
free mailers already do to some extent as you have an associated address
book. Some start doing possible matches as you type. I hazard Rich is not
using something this simple as he does seem to have some form-letter merge
or similar functionality in mind, such as automating the seemingly mandatory
"Dear XXX" salutation.

But if he is the creator and maintainer of his client data and chooses not
to use one of many available applications, then it seems he already has
reasons he wants a particular design for the data and simply wants us to
help him use it the way he wants. That could be communicated a bit more
clearly but after many messages back and forth, I have not exactly
understood it.

In my opinion, having created all kinds of mailers over the years, sometimes
the hard way, This strikes me as not really being about what mailing
functionality exists at all. As a general rule, you first create supporting
parts for your mail then pass them along to functionality that assembles the
mail as a set of headers and a body and dispatches it.

You as the programmer need to supply a body, tell it who to put on TO/CC/BB
lines, perhaps provide a subject, perhaps specify attachments, and off you
go. The exact methods will differ.

But what Rich presumably needs to do is have his program interact with him
in specifying who he wants to mail to and then looking it up in whatever
file arrangement it contains. If he also wants to use other parts such as a
human name or address inside the body of the text, his program needs to
merge the text he supplies along with extracted parts of the data.

Or is that not what he wants? The above could be quite straightforward and I
recall doing things like this with a simple shell script in UNIX.
Specifically, I created a text file where I recorded info for each person in
some format like

NAME|PHONE|EMAIL|COMMENT

Then to search for someone, you could use something like grep to find a name
by anchoring to the beginning or ending with the "|" so it does not match
the text in another field such as email or address, and use other utilities
ranging from cut to awk and getting the parts you want into variables and
then interpolate them into a message template and so on.

Of course, doing it in python is a good way to go too and should not be hard
once it is decided how to store the data. But again, this is re-inventing
things that others have already done. 

The python modules include many ways to store modular data. The books I have
read mention them all the time. Pick one. And, yes, you can choose to
maintain two files if that design works for you. Consider some storage
method that stores data in sections like:

[NAME one]
First: whatever
Email: whatever

[NAME two]
First: ...
Email: ...

There are specific formats along these lines and you can get python modules
that you ask for "NAME one" and it reads the file until it finds a section
as "[NAME one]" or not. If found, it returns the variables/values right
below it.  So your two step algorithm may consist of two files with one file
containing just names, perhaps to use a grep functionality on. Some of those
names will have a matching section like the above somewhere in the other
file. 

So if you want to send mail to "Jo" then your program may search for all
names starting with "Jo" and offer you "John Smith"  and perhaps also
"Joachim Martillo". The program takes whichever full name(s) you then select
and calls a function that uses that full name to search the second file to
find an exact match and returns what it finds there such as an email
address.

But unless you have lots of contacts, as already discussed, there are far
easier ways to do things in a more brute force way. Take a one-line per
entry format such as a CSV or TSV and extract whatever column contains the
name as needed to do the first search. Yes, this tends to mean reading the
entire file.

And, for the record, I am not a fan of hiding replies at the bottom except
for short messages. I prefer to use some combination of in-line if
addressing many points in the original and mainly the top with perhaps a
preface explaining what is being addressed. The reader is usually capable of
digging below if they want to know more. But this is a more religious war
having nothing to do with python specifically.

My frustration is that I often want to help 

Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/30/2024 8:37 AM, Rich Shepard via Python-list wrote:

On Mon, 29 Jan 2024, Thomas Passin via Python-list wrote:


If you aren't going to use one or another existing template system,
perhaps the easiest is to use unique strings in the message file. For
example:

Dear __##so-and-so##__:
  Please don't write this message off as mere spam.
  Respectfully, Rich

Then you just do a replace of the unique string by the salutation. Don't
change the original (i.e., template), make the changes to a copy that you
will output.


My script is not a web application, but an emailer that allows me to 
contact

clients and prospective clients. From the command line on a linux host.
Using the python smtplib and mail modules.

Rich


Fine, my toy example will still be applicable.  But, you know, you 
haven't told us enough to give you help.  Do you want to replace text 
from values in a file?  That's been covered. Do you want to send the 
messages using those libraries?  You haven't said what you don't know 
how to do.  Something else? What is it that you want to do that you 
don't know how?


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Re: Extract lines from file, add to new files

[Larry Martell via Python-list]

On Tue, Jan 30, 2024 at 1:13 AM AVI GROSS via Python-list
 wrote:
>
> It can be quite frustrating figuring out what someone wants, Grant,
> especially when they just change it.
>
> It is worse when instead of starting a new thread with an appropriate
> subject line, it continues and old one that was also frustrating to
> understand.

Is it worse than top posting?
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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Mon, 29 Jan 2024, Thomas Passin via Python-list wrote:


If you aren't going to use one or another existing template system,
perhaps the easiest is to use unique strings in the message file. For
example:

Dear __##so-and-so##__:
  Please don't write this message off as mere spam.
  Respectfully, Rich

Then you just do a replace of the unique string by the salutation. Don't
change the original (i.e., template), make the changes to a copy that you
will output.


My script is not a web application, but an emailer that allows me to contact
clients and prospective clients. From the command line on a linux host.
Using the python smtplib and mail modules.

Rich
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

It can be quite frustrating figuring out what someone wants, Grant,
especially when they just change it.

It is worse when instead of starting a new thread with an appropriate
subject line, it continues and old one that was also frustrating to
understand.

It sounds though like another attempt to do something perhaps a different
way. Both attempts seem to be to use some form of storage of a set of email
addresses plus other info like a name that can be used to make a customized
email.

Frankly, this should have been fairly easy to do without so much back and
forth. I don't care how the email is actually sent, but the rest could have
been done any number of ways such as storing the data as rows in a CSV file
or saved using JSON format and so on. It was never made clear why two files
were needed and then somehow linked and searched. 

If the goal is to be able to search for something like a name and THEN find
an email address, that seems quite trivial if they are I the same file in
some format. If the number of items is small, reading it all in should not
be a big deal and you can use a regular expression or other method to locate
the entry you want and extract the additional info. If you have lots of
data, reading line after line may be less useful than just using a database
and a query.

One way to stop feeling frustrated is to stop reading the thread.

-Original Message-
From: Python-list  On
Behalf Of Grant Edwards via Python-list
Sent: Monday, January 29, 2024 5:54 PM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On 2024-01-29, Rich Shepard via Python-list  wrote:
> On Mon, 29 Jan 2024, Rich Shepard via Python-list wrote:
>
>> No, I hadn't ... but I am reading it now.
>
> Perhaps I missed the answer to my question when reading the io module. It
> explains how to open/write/read files of text and binary data, not passing
> a variable's value from one file to a place-keeper in another file.

It's not at all clear (to me) what you're asking about.  When you talk
about "files" are you referring to data files? Python modules within a
single program? Seperate Python programs?  Something else?

The phrase "place-keeper in another file" sounds a bit like you're
trying to do templating. There are many, many ways to do templating in
Python -- ranging from literal 'f-strings' to powerful templating
engines that are used to construct entire web sites:

  https://www.google.com/search?q=python+templating

  https://docs.python.org/3/tutorial/inputoutput.html#tut-f-strings

  https://en.wikipedia.org/wiki/Jinja_(template_engine)

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Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/29/2024 11:15 AM, Rich Shepard via Python-list wrote:

For my use 1) the salutation and email address (always with an '@') are
sequential and 2) I'm developing the script to extract both from the same
file.


I've looked at my Python books "Python Crash Course," "Effective Python,"
and "Python Tricks The Book" as well as web pages in my searches without
finding the answer to what may be a simple question: how to specify a
variable in one file that has its values in another file.

Specifically, how to I designate the salutation holder in the message file
and pass it the name value from the name/email address file?

If this explanation is not sufficiently clear I'll re-write it. :-)

TIA,

Rich


I'm assuming this is a continuation of a previous thread about working 
with alternate lines with salutation and address, and I assume you've 
got that worked out.


If you aren't going to use one or another existing template system, 
perhaps the easiest is to use unique strings in the message file.  For 
example:


Dear __##so-and-so##__:
   Please don't write this message off as mere spam.
   Respectfully, Rich

Then you just do a replace of the unique string by the salutation. Don't 
change the original (i.e., template), make the changes to a copy that 
you will output.


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Re: Extract lines from file, add to new files

[Grant Edwards via Python-list]

On 2024-01-29, Rich Shepard via Python-list  wrote:
> On Mon, 29 Jan 2024, Rich Shepard via Python-list wrote:
>
>> No, I hadn't ... but I am reading it now.
>
> Perhaps I missed the answer to my question when reading the io module. It
> explains how to open/write/read files of text and binary data, not passing
> a variable's value from one file to a place-keeper in another file.

It's not at all clear (to me) what you're asking about.  When you talk
about "files" are you referring to data files? Python modules within a
single program? Seperate Python programs?  Something else?

The phrase "place-keeper in another file" sounds a bit like you're
trying to do templating. There are many, many ways to do templating in
Python -- ranging from literal 'f-strings' to powerful templating
engines that are used to construct entire web sites:

  https://www.google.com/search?q=python+templating

  https://docs.python.org/3/tutorial/inputoutput.html#tut-f-strings

  https://en.wikipedia.org/wiki/Jinja_(template_engine)

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Re: Extract lines from file, add to new files

[dn via Python-list]

On 30/01/24 05:15, Rich Shepard via Python-list wrote:

On Fri, 12 Jan 2024, Rich Shepard via Python-list wrote:


For my use 1) the salutation and email address (always with an '@') are
sequential and 2) I'm developing the script to extract both from the same
file.


I've looked at my Python books "Python Crash Course," "Effective Python,"
and "Python Tricks The Book" as well as web pages in my searches without
finding the answer to what may be a simple question: how to specify a
variable in one file that has its values in another file.

Specifically, how to I designate the salutation holder in the message file
and pass it the name value from the name/email address file?

If this explanation is not sufficiently clear I'll re-write it. :-)



It seems clear - but maybe we (all) misunderstand?

The books don't cover it - but is there a reason why they don't?


(Thunderbird did not thread this message with earlier ones, and it seems 
some time has passed/memory is fading - but hopefully have remembered 
content)



As said previously, the idea of two physical-files containing 
logically-related data (without any form of cross-reference between) is 
bad design.


In the current file, there is one physical structure and each person's 
details are logically-related by proximity. A long way from ideal, but 
workable (as you've described).


However, once split into two files, there is no way to guarantee that 
the two logically-related data-items (name and address) will continue to 
be related by their physical position in the respective files. Worse: 
whilst it would seem apparent that "Alice" from the names file might be 
related to the address "al...@domain.tld", how could one know if "Bob" 
actually corresponds to "list-mem...@domain.tld"?


This is why dicts, databases, etc, offer keys (as labels for 
data-items/dependent components)!



After a quick look at Eric's Crash Course, yes, his files-intro example 
(digits of pi) is unlikely to have any practical reality (and I work 
with statisticians and quants!). However, at the end of that chapter 
(10), there is mention of JSON files. A JSON version of the existing 
single-file structure will provide human-readable labeling of 
data-items, give better separation between individuals' data, and show 
how name and address are linked. Recommend solving 'the problem' that 
way! (as previously discussed by others 'here', IIRC)


Slatkin's Effective Python doesn't seem to discuss the basics of files 
at all (presumes such knowledge of the reader). It dives into important, 
but rather technical discussions, comparing strings and bytes - somewhat 
beyond the complexity-level of this discussion. That book does however 
include discussions such as "Prefer Multiple Assignment Unpacking over 
Indexing" (Item 6 - also points to Item 19) where relative-positioning 
(indexing in other words) is advised-against.



If you wish to persist with this two-file structure, please see earlier 
responses (again, IIRC) and discussion of file-merge operations. As 
these date back to mainframes and the days of storing files on mag-tape, 
I'd be surprised to see them discussed in 'modern' texts. However, the 
principle is: read a record from each file, do-the-business, read the 
next 'pair' of physically-related records, rinse-and-repeat.


If you require further assistance: how about showing a couple of 
relevant lines of the data-file(s) and the pertinent parts of the code, 
along with a description of what's going-wrong or not making sense to you?


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=dn
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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Mon, 29 Jan 2024, avi.e.gr...@gmail.com wrote:


There are several general solutions that may apply. Some involve reading
in both files into data structures and perhaps linking them together in
some way such as a data.frame or binary tree. You can then process
individual request in memory/


Avi,

I found several web pages describing how to use the python email library and
tools to send individual or multiple email messages. I'll learn how to do
this based on a couple of detailed examples.

Thanks,

Rich
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Rich,

You got an overly general reply to a question many of us may not understand.

You have not hinted at how the two files are organized, perhaps with an
example.

There are several general solutions that may apply. Some involve reading in
both files into data structures and perhaps linking them together in some
way such as a data.frame or binary tree. You can then process individual
request in memory/

The second should be straightforward as long as text is text. If the first
file tells you to search for XYZ then you search the second file for XYZ and
read in whatever is associated with it and do your thing.

Without a bit more specific detail, you may not get more than a suggestion
as to how to read in files.


-Original Message-
From: Python-list  On
Behalf Of Rich Shepard via Python-list
Sent: Monday, January 29, 2024 12:38 PM
To: python-list@python.org
Subject: RE: Extract lines from file, add to new files

On Mon, 29 Jan 2024, Rich Shepard via Python-list wrote:

> No, I hadn't ... but I am reading it now.

Perhaps I missed the answer to my question when reading the io module. It
explains how to open/write/read files of text and binary data, not passing
a variable's value from one file to a place-keeper in another file.

I'll keep searching for a solution.

Rich
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RE: Extract lines from file, add to new files [RESOLVED]

[Rich Shepard via Python-list]

On Mon, 29 Jan 2024, Rich Shepard via Python-list wrote:


I'll keep searching for a solution.


IIRC, someone here pointed me to 
and I forgot about it ... until now.

Regards,

Rich
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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Mon, 29 Jan 2024, Rich Shepard via Python-list wrote:


No, I hadn't ... but I am reading it now.


Perhaps I missed the answer to my question when reading the io module. It
explains how to open/write/read files of text and binary data, not passing
a variable's value from one file to a place-keeper in another file.

I'll keep searching for a solution.

Rich
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RE: Extract lines from file, add to new files

[Dieter Maurer via Python-list]

Rich Shepard wrote at 2024-1-29 08:15 -0800:
> ...
>If this explanation is not sufficiently clear I'll re-write it. :-)

Have you read "https://docs.python.org/3/library/io.html#module-io;?

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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Mon, 29 Jan 2024, dieter.mau...@online.de wrote:


Have you read "https://docs.python.org/3/library/io.html#module-io;?


Dieter,

No, I hadn't ... but I am reading it now.

Many thanks,

Rich
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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Fri, 12 Jan 2024, Rich Shepard via Python-list wrote:


For my use 1) the salutation and email address (always with an '@') are
sequential and 2) I'm developing the script to extract both from the same
file.


I've looked at my Python books "Python Crash Course," "Effective Python,"
and "Python Tricks The Book" as well as web pages in my searches without
finding the answer to what may be a simple question: how to specify a
variable in one file that has its values in another file.

Specifically, how to I designate the salutation holder in the message file
and pass it the name value from the name/email address file?

If this explanation is not sufficiently clear I'll re-write it. :-)

TIA,

Rich
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Re: Extract lines from file, add to new files

[Antoon Pardon via Python-list]

Op 14/01/2024 om 13:28 schreef Left Right via Python-list:

Python isn't a context-free language, so the grammar that is used to
describe it doesn't actually describe the language... so, it's a
"pretend grammar" that ignores indentation.


No it doesn't. Here is the definition of a block, it clearly mentions
indentation:

block:
|  NEWLINE INDENTstatements  DEDENT
|  simple_stmts But you are correct that python in not a context-free 
language. But so is any programming language. Yet a lot of those non 
context-free language designers thought it helpful to have a 
modified/extended BNF description of a superset of the intended language 
and used other means to further check whether the code in question was 
valid or not. -- Antoon Pardon

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Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 21:13, Greg Ewing via Python-list wrote:

On 15/01/24 1:54 pm, dn wrote:

Soon after, Wirth simplified rather than expanded, and developed Pascal.


Before Pascal there was Algol-W, which Wirth invented as a rebellion
against how complicated Algol 68 was becoming.

When I first saw this I was stunned, then attracted to its simplicity, 
but then steered-away once realised that it needed 'more' to cope with 
'the outside world'.


Pascal was intended as a teaching language, and as such it was lacking
in practicality in a few spots. But it didn't need much tweaking to
make it a very useful language. UCSD Pascal, Turbo Pascal, Delphi, etc.
enjoyed a lot of popularity. A variant of UCSD was the main language
for Macintosh application development for a number of years.



Ironically, I didn't come across Pascal as a teaching-language.

Borland were trying to turn Turbo Pascal into a practical development 
environment, beyond teaching (as with others of their 'Turbo' series). 
As I say, it didn't float my business-world boat.
- not before I won a case a wine from Philippe Kahn's own vineyard for 
solving some 'interview question' and exchanging jokes with him, in 
French, at some Trade Show in London. Two surprises: one, that it 
actually turned-up a few weeks later, and two, that I (suddenly) had so 
many friends!


Ah, the good, old days...


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=dn
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 19:26, Greg Ewing via Python-list
 wrote:
>
> On 15/01/24 9:07 pm, Chris Angelico wrote:
> > The grammar *can't* specify everything. If it did, it would have to
> > have rules for combining individual letters into a NAME and individual
> > characters into a string literal.
>
> The lexical level of a grammar can be, and often is, described
> formally using regular expressions.
>
> Although some might consider that this doesn't contradict
> your statement about readability. :-)
>

Not even slightly :)

ChrisA
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 15/01/24 9:07 pm, Chris Angelico wrote:

The grammar *can't* specify everything. If it did, it would have to
have rules for combining individual letters into a NAME and individual
characters into a string literal.


The lexical level of a grammar can be, and often is, described
formally using regular expressions.

Although some might consider that this doesn't contradict
your statement about readability. :-)

--
Greg
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 15/01/24 1:54 pm, dn wrote:
Soon after, Wirth simplified 
rather than expanded, and developed Pascal.


Before Pascal there was Algol-W, which Wirth invented as a rebellion
against how complicated Algol 68 was becoming.

When I first saw this I was 
stunned, then attracted to its simplicity, but then steered-away once 
realised that it needed 'more' to cope with 'the outside world'.


Pascal was intended as a teaching language, and as such it was lacking
in practicality in a few spots. But it didn't need much tweaking to
make it a very useful language. UCSD Pascal, Turbo Pascal, Delphi, etc.
enjoyed a lot of popularity. A variant of UCSD was the main language
for Macintosh application development for a number of years.

--
Greg
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 18:56, Greg Ewing via Python-list
 wrote:
>
> On 15/01/24 1:28 am, Left Right wrote:
> > Python isn't a context-free language, so the grammar that is used to
> > describe it doesn't actually describe the language
>
> Very few languages have a formal grammar that *fully* describes
> the set of strings that constitute valid programs, including all
> the rules about things having to be declared, types matching up,
> etc. The only one I know of which attempted that is Algol 68,
> and it seems to be regarded as a technical success but a practical
> failure.
>
> > ... so, it's a "pretend grammar" that ignores indentation.
>
> Indentation isn't ignored, it appears in the grammar by means of
> INDENT and DEDENT lexical tokens.
>
> It's true that the meaning of these tokens is described informally
> elsewhere, but that's true of all the lexical features.
>

I've recently been doing a bit of work with grammar parsers, and to be
quite honest, the grammar is only about one third of the overall
parser.  There are three sections with roughly equal importance:

1. Tokenizer
2. Grammar
3. What to DO with that grammar (actions)

INDENT and DEDENT are being handled at the tokenizer stage, and so are
a lot of other rules like backslashes in quoted strings. On the flip
side, string prefixes (like b"...") seem to be handled in the third
phase, and the grammar actually doesn't concern itself with those
either.

The grammar *can't* specify everything. If it did, it would have to
have rules for combining individual letters into a NAME and individual
characters into a string literal. The grammar would be completely
unreadable. (I tried, and even just building up a decimal literal in
that style was quite a pain.)

ChrisA
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 15/01/24 1:28 am, Left Right wrote:

Python isn't a context-free language, so the grammar that is used to
describe it doesn't actually describe the language


Very few languages have a formal grammar that *fully* describes
the set of strings that constitute valid programs, including all
the rules about things having to be declared, types matching up,
etc. The only one I know of which attempted that is Algol 68,
and it seems to be regarded as a technical success but a practical
failure.


... so, it's a "pretend grammar" that ignores indentation.


Indentation isn't ignored, it appears in the grammar by means of
INDENT and DEDENT lexical tokens.

It's true that the meaning of these tokens is described informally
elsewhere, but that's true of all the lexical features.

--
Greg
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 13/01/24 11:34 pm, Left Right wrote:

To make this
shorter, Python allows:

for  in ... : ...



Um, no, it doesn't. An assignment target is not, on its own, a
statement.

It's hard to make sense of what you're saying. You seem to be
surprised by the fact that Python doesn't require variables to
be declared separately from their use. But this is a very common
feature of dynamic languages generally. As language oddities go,
it hardly rates a mention.

--
Greg
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 14:45, Chris Angelico wrote:

On Mon, 15 Jan 2024 at 12:42, dn via Python-list  wrote:


On 15/01/24 14:33, Chris Angelico via Python-list wrote:

On Mon, 15 Jan 2024 at 12:12, dn via Python-list  wrote:

Here's another witticism I'll often toss at trainees (in many languages,
and especially in UX): just because we can do it, doesn't make it a good
idea!



Programming. We were so busy with whether we COULD that we didn't stop
to think if we SHOULD.

I think that's basically my whole life.


Don't be too hard on yourself.

My life-advice has always been "don't do anything I wouldn't do"
- which pretty-much gives you carte blanche.



I would NEVER give that advice to anyone. They would leave the dishes
unwashed, and a number of other problems :)


I'd soon have you sorted-out - except for one small problem: all the 
dishes have been done!


If you can get here before the rain, the lawn needs mowing...

--
Regards,
=dn

--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 12:42, dn via Python-list  wrote:
>
> On 15/01/24 14:33, Chris Angelico via Python-list wrote:
> > On Mon, 15 Jan 2024 at 12:12, dn via Python-list  
> > wrote:
> >> Here's another witticism I'll often toss at trainees (in many languages,
> >> and especially in UX): just because we can do it, doesn't make it a good
> >> idea!
> >>
> >
> > Programming. We were so busy with whether we COULD that we didn't stop
> > to think if we SHOULD.
> >
> > I think that's basically my whole life.
>
> Don't be too hard on yourself.
>
> My life-advice has always been "don't do anything I wouldn't do"
> - which pretty-much gives you carte blanche.
>

I would NEVER give that advice to anyone. They would leave the dishes
unwashed, and a number of other problems :)

ChrisA
-- 
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 14:33, Chris Angelico via Python-list wrote:

On Mon, 15 Jan 2024 at 12:12, dn via Python-list  wrote:

Here's another witticism I'll often toss at trainees (in many languages,
and especially in UX): just because we can do it, doesn't make it a good
idea!



Programming. We were so busy with whether we COULD that we didn't stop
to think if we SHOULD.

I think that's basically my whole life.


Don't be too hard on yourself.

My life-advice has always been "don't do anything I wouldn't do"
- which pretty-much gives you carte blanche.

--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 12:12, dn via Python-list  wrote:
> Here's another witticism I'll often toss at trainees (in many languages,
> and especially in UX): just because we can do it, doesn't make it a good
> idea!
>

Programming. We were so busy with whether we COULD that we didn't stop
to think if we SHOULD.

I think that's basically my whole life.

ChrisA
-- 
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 11:47, Chris Angelico via Python-list wrote:

On Mon, 15 Jan 2024 at 09:40, dn via Python-list  wrote:

The basic challenge came from my earlier (and blasé) repetition of the
Python refrain "everything in Python is an object". Which led to:

...


So, no, there's an "everything" which (might be) an object but which
cannot be used in that scenario.


More accurately, every VALUE in Python is an object. This does not
mean that syntax is an object. Very few languages would say that every
single grammatical element is a value.


+1

Thank you. This old-dog will try to re-learn that term...



Yes, it's sloppy to say "everything" is an object, but it's also
rather nonintuitive to claim that, therefore, syntax elements are all
objects. It's like claiming that everything that this dealership sells
is a car (or "everything in this dealership is a car"), and therefore
the dealership's name must itself be a car.


To say nothing of 'extended warranties'!
(and their dubious rationale)



That said, does anyone think that something like:

  for a_function( etc ) in iterable/iterator:

is acceptable?
- see both Python definition and (full-)quotation.

I've not come-across a language which does allow such - YMMV/mea culpa;
and am struggling to see how it could possibly be useful.


You could do something close to that:

for a_function(etc)[0] in iterable: ...

because an assignment target can contain an arbitrary expression
followed by the subscript.


Here's another witticism I'll often toss at trainees (in many languages, 
and especially in UX): just because we can do it, doesn't make it a good 
idea!




* Looking at the correspondent's email-address (cf 'handle') - and as an
unfair stereotype, raises the question of issues related to (English)
language-skills - which, arrogantly implies/assumes that native
English-speakers are all highly-capable. (?) A negative-interpretation
is to note his apparent intelligence, but wonder if failing to represent
others' comments fairly is deliberate, or carelessness. Is there an
irony in behaving/failing in such, whilst attempting to hold Python's
structure to some golden-ideal?


Seems likely.



--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 08:06, AVI GROSS via Python-list wrote:
...> You provided a way to create an anonymous function and that was not 
enough.

I wonder if you could throw in the new := walrus operator to similarly make
a named lambda function in a similar way.


Why would @Chris have anything to do with the 'walrus-operator'?

PS our interlocutor doesn't like colloquialisms such as these - despite 
them being near-and-dear to our hearts!


--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 01:28, Left Right wrote:

Second time to ameliorate wording-dispute in this thread! The original
phrase was: "[modified] BNF". Some of us have worked with various forms
and evolutions of BNF since back in the days of COBOL-60 proposals, and
know it when we see it!


OK, here are the conceptual differences between what Python grammar
language does and what you'd expect from anything that's based on BNF,
modified or not:

Python isn't a context-free language, so the grammar that is used to
describe it doesn't actually describe the language... so, it's a
"pretend grammar" that ignores indentation.  BNF is supposed to be
used to describe the language, it's not a "pretend" or "pseudo"
grammar, in a way we have at least two established grammar for
pseudo-code.

BNF and derivatives don't have an inherent mechanism for tiebreaks.
The mechanism is necessary because BNF rules can be tried in any
order.  Some grammar languages derived from BNF declare ambiguous
grammars invalid, some allow ambiguity, but say that the longest
prefix wins, and if there's still ambiguity after that, then such
grammar is invalid, some have special constructs to define "priority"
etc. My reading of Python grammar is that it works like PEG, where
rules are tried in the order they are defined.  This makes it less
expressive, but easier to work with.  This is, probably, the most
fundamental difference between the BNF family and the PEG family.

BNF and family languages rarely incorporate elements of Perl-like
regular expression parsing in the language (i.e. things like
lookaheads, lookbehinds etc.) This is more typical of the PEG family.

On top of this, the Python grammar language has a bunch of
"inventions" that are unique to it (I've never seen any other grammar
language use '.' in the same way Python uses it).  So, there's that
too.

Having worked with a bunch of different grammar languages, the one
used for Python isn't a recognizable BNF derivative.  I think the
authors used this as a description in the same way as today a lot of
programmers would use the word "IDE" to describe any text editor or
"REST" to describe any kind of server-client protocol over HTTP and so
on.  Or, how we'd use "Xerox" to name a copier machine, even if that
company didn't manufacture it, and even if the tech used for copying
is completely different.  And that's why I wrote that the grammar is
actually more like PEG, adding that it's neither, but seems to fall
more into that later category.


We are in broad-agreement. I'd enjoy the discussion, except that I can't 
see where it is leading or how it will benefit you...


Where we seem to differ is the length of time we've been part of the 
Python-world.


An important point is that languages are often described as 'living', 
because they evolve over time. I'm relieved to note that the youngsters 
in the family have stopped describing 'everything' as "awesome". That 
word, has taken-on aspects of the original meanings of "awful". The 
former being positive-factors, and the negative ascribed to the latter. 
However, we don't have to step far back into history to find that 
"awful" meant 'full of awe' or awe-inspiring - with no connotation of 
'good' or 'bad'. There was no need for a word with opposite-meaning, 
apart from "mundane".


Similarly, spoken-language often lacks precision. My CO, to this day, 
uses phrases like "all done" [with time for me to take a breath, 
followed by "except ...", eg "are we ready to leave for ...?". This 
drives me nuts. (the word "nuts" requires consideration too!) Thus, have 
learned to elicit the pertinent information with phrasing such as "what 
is left to be done?" rather than arguing the illogic between "all" and 
"except".


Python is not different. We're currently looking at version 3.12, which 
implies three major iterations of the language. Accordingly, when it was 
a 'green fields project', what may have been a pure and elegant 
expression of a language, has become "acquisitive". Sometimes these 
additions-and-alterations have required compromise, eg lack of elegance. 
Sometimes, it has been realised that there is a flaw, and things need to 
be improved, even removed.


You've made comments about BNF. Like Python, it is a 'language' (a bit 
of stretch, but...) which has also been pulled, poked, and perhaps 
contorted over time. It had a body of folk who understood its 
expression, and therefore it made sense to stick with some variation of 
it (even warts-and-all) rather than going with something 'new'.



All of which creates the sorts of issues described.

The PEG-parser is a comparatively-recent improvement - other aspects 
previously-mentioned.


I'm not going to touch "Perl".

Is there really some sort of standard-understanding/format for 
"pseudo-code"? (ISO?)


Yes, there's some 'pretense' (not sure I'd choose that exact term). 
However, it is working for the vast-majority. Perhaps after using Python 
for so long, I'm comfortable accepting such 

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Whoa, Олег Сивоконь!

I do not understand any arguments about whether comments are, or are not an
object.

From one perspective, python comments have even less meaning than whitespace
and simply do not exist. I mean once a naked "#" is seen, the rest of that
line is effectively discarded by the interpreter. The supposed multi-line
comments though, meaning something like a triple set of quotes up to another
set are probably objects in the sense that they create a text literal in a
context where there is no usual pointer to them and are thus largely ignored
and perhaps garbage collected. Some programs look for them in code as part
of documentation and it is possible they are stored in some object that
"holds" aspects of a function.

But I think that talking about some inconsistency in python because comments
are not an object is a bit silly. Why should they be? If I choose to leave
lots of blank lines between my function definitions or statements, do they
need to be made into an object, or ignored as superfluous but legal
whitespace?

I have seen many debates about some form of purity and generally, they get
boring. Nobody in their right mind can defend any computer language as being
100% right for every purpose. Python has some reasonable tradeoffs and is
highly popular and there are other languages with other tradeoffs you can
use instead. At this point, making changes without disrupting things gets
ever harder.

-Original Message-
From: Python-list  On
Behalf Of Left Right via Python-list
Sent: Sunday, January 14, 2024 7:28 AM
To: Chris Angelico 
Cc: python-list@python.org
Subject: Re: Extract lines from file, add to new files

> Second time to ameliorate wording-dispute in this thread! The original
> phrase was: "[modified] BNF". Some of us have worked with various forms
> and evolutions of BNF since back in the days of COBOL-60 proposals, and
> know it when we see it!

OK, here are the conceptual differences between what Python grammar
language does and what you'd expect from anything that's based on BNF,
modified or not:

Python isn't a context-free language, so the grammar that is used to
describe it doesn't actually describe the language... so, it's a
"pretend grammar" that ignores indentation.  BNF is supposed to be
used to describe the language, it's not a "pretend" or "pseudo"
grammar, in a way we have at least two established grammar for
pseudo-code.

BNF and derivatives don't have an inherent mechanism for tiebreaks.
The mechanism is necessary because BNF rules can be tried in any
order.  Some grammar languages derived from BNF declare ambiguous
grammars invalid, some allow ambiguity, but say that the longest
prefix wins, and if there's still ambiguity after that, then such
grammar is invalid, some have special constructs to define "priority"
etc. My reading of Python grammar is that it works like PEG, where
rules are tried in the order they are defined.  This makes it less
expressive, but easier to work with.  This is, probably, the most
fundamental difference between the BNF family and the PEG family.

BNF and family languages rarely incorporate elements of Perl-like
regular expression parsing in the language (i.e. things like
lookaheads, lookbehinds etc.) This is more typical of the PEG family.

On top of this, the Python grammar language has a bunch of
"inventions" that are unique to it (I've never seen any other grammar
language use '.' in the same way Python uses it).  So, there's that
too.

Having worked with a bunch of different grammar languages, the one
used for Python isn't a recognizable BNF derivative.  I think the
authors used this as a description in the same way as today a lot of
programmers would use the word "IDE" to describe any text editor or
"REST" to describe any kind of server-client protocol over HTTP and so
on.  Or, how we'd use "Xerox" to name a copier machine, even if that
company didn't manufacture it, and even if the tech used for copying
is completely different.  And that's why I wrote that the grammar is
actually more like PEG, adding that it's neither, but seems to fall
more into that later category.

> Yes it is hard to read - and even harder to learn-from;

This wasn't my point.  My point is that it's hard to learn languages
that are "one off" in the group languages that all share a similar set
of rules. The difficulty comes from the surprise caused by the unique
use, not because there's something inherently difficult about reading
grammar languages.  In fact, however you look at Python's grammar
language, in a sense, it's a lot easier to read than Python itself
because it has significantly fewer rules.  Of course, the number of
rules doesn't entirely capture the difficulty, but it's a useful
metric.

> In Python, everything is an object. As long as the LHS is a legal-object
> which  makes sense for the situat

Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 09:40, dn via Python-list  wrote:
> The basic challenge came from my earlier (and blasé) repetition of the
> Python refrain "everything in Python is an object". Which led to:
>
> <<<
> For example, you may say "functions in Python are
> objects", but you cannot put a function definition in the head of the
> for loop clause.
>  >>>
>
> Which is logical - to some degree, and in-isolation.
>
>  for def a_function( etc )... in iterable/iterator:
>
> does not make sense. The 'head' (a more generic name, where Python says
> "target_list", that refines down to 'something which can identify the
> generated-value'.
>
> So, no, there's an "everything" which (might be) an object but which
> cannot be used in that scenario.

More accurately, every VALUE in Python is an object. This does not
mean that syntax is an object. Very few languages would say that every
single grammatical element is a value.

Yes, it's sloppy to say "everything" is an object, but it's also
rather nonintuitive to claim that, therefore, syntax elements are all
objects. It's like claiming that everything that this dealership sells
is a car (or "everything in this dealership is a car"), and therefore
the dealership's name must itself be a car.

> That said, does anyone think that something like:
>
>  for a_function( etc ) in iterable/iterator:
>
> is acceptable?
> - see both Python definition and (full-)quotation.
>
> I've not come-across a language which does allow such - YMMV/mea culpa;
> and am struggling to see how it could possibly be useful.

You could do something close to that:

for a_function(etc)[0] in iterable: ...

because an assignment target can contain an arbitrary expression
followed by the subscript.

> * Looking at the correspondent's email-address (cf 'handle') - and as an
> unfair stereotype, raises the question of issues related to (English)
> language-skills - which, arrogantly implies/assumes that native
> English-speakers are all highly-capable. (?) A negative-interpretation
> is to note his apparent intelligence, but wonder if failing to represent
> others' comments fairly is deliberate, or carelessness. Is there an
> irony in behaving/failing in such, whilst attempting to hold Python's
> structure to some golden-ideal?

Seems likely.

ChrisA
-- 
https://mail.python.org/mailman/listinfo/python-list

RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Straight Ahead, on average,

I am not sure what your beef is as apparently it is always something else than 
some others assumed.

If your point is that you want consistency, sure that would be nice. But maybe 
part of the inconsistency I am not sure you mean is an artifact of the language.

There are programming languages where a keyword like "def" is used to create a 
function and similarly some where variables are declared some special way like 
"let" or "var" and "const" or "class" to provide the right hints. Some 
languages skip that and just let you pop up a variable as in "x=5" both 
declares and instantiates a variable. Strictly speaking, in a language like 
python, everything is an object and some of the way of creating them remains 
bound to other ideas like declaring a class uses key words as does declaring a 
function. 

But consider a language like R which declares a function similar to anything 
else:

X <- 5
Times2 <- function(x) { x*2 }

The keyword has been moved as compared to the python:

Def Times2(x):
return(x*2)

It is not a question of being better or worse, but simply speaking, there is no 
special keyword to start the process before the name, but rather a keyword 
later that is really similar to a lambda method. Secondarily, not relying on 
indentation, may make it easier in some cases to insert the function 
declaration anywhere a statement might fit as there is no special keyword.

Other languages have their own chosen ways and many will fail various tests you 
can come up with.

Could python have chosen some other way that would have fit some grammar needs? 
Probably. But it did not.

If you want to play a common grammar game, you can define a higher-level 
construct I will simply call A  that is decomposed into two or more subcontexts 
one of which is B and then populate the tree on each side with more and more 
specific stuff. Then when talking about what is allowed in context alpha, where 
all expressions are allowed, say it supports A or anything in the tree below 
it. In another context, say it only supports B and anything below that.

Think of it a bit like subclassing.

Perhaps you can then build a complex description that can be instantiated by 
code to define all valid programs from invalid ones. But it would remain a pain 
to implement all the tools you want to help you, including in an editor or 
programming environment, where figuring out the context may become very 
difficult.

Still, making things very loose and general so that your design looks simple 
has many negative tradeoffs too, including allowing rather nonsensical things.

People who create programming languages have various goals in mind that guide 
what they choose. Python was not made to be a mathematically perfect object 
that guided being able to have programs proven to work and so on. It is 
acknowledged various aspects do not please some people or others and I am not 
defending it.

I am wondering if what is being discussed is in any way a serious issue.

The original question in this thread really was a minor one and how it became 
whatever this is, well, I give up! LOL!


-Original Message-
From: Left Right  
Sent: Sunday, January 14, 2024 4:15 PM
To: avi.e.gr...@gmail.com
Cc: Chris Angelico ; python-list@python.org
Subject: Re: Extract lines from file, add to new files

> You said function. I made a function. You said "head of a for loop
> clause". I put it there. Problem was underspecified.

I also wrote a lot of letters, if you combine them very liberally,
without any regard to the order in which they were written or the
context in which they were used, you may come up with very surprising
findings.

> But if you're trying to tell me that a def statement should be a valid
> assignment target,

Why not just read what I wrote and work from there?  No, I didn't
write anything even remotely similar to this...  I don't want function
definition to be an assignment target.  I was giving an example of how
Python grammar works, how the rules govern what can or cannot be used
in a particular place...

In other words, if you aren't sure you understand the question, why
are you trying to reply to it? Is your goal to learn the meaning of
the question by giving arbitrary replies and hoping that the author of
the question restates it so that you understand it?  If so, I believe,
the better strategy would be to simply ask to restate the question.
Will save you the round-trip.

> You provided a way to create an anonymous function and that was not enough.
> I wonder if you could throw in the new := walrus operator to similarly make
> a named lambda function in a similar way.

The person you are replying to didn't understand the question and has
written something irrelevant.  It's not about being "enough".  I
honestly don't know why they are spending so much energy replying to
my messages :|

Re: Extract lines from file, add to new files

[dn via Python-list]

On 15/01/24 10:23, Chris Angelico via Python-list wrote:

On Mon, 15 Jan 2024 at 08:15, Left Right  wrote:

Python grammar rules prevent function definition from
appearing in left-hand side of the head of the for loop.  However, a
variable declaration, which is also a statement, is allowed there.


What is a "variable declaration" in Python? Please elaborate.


We may be in danger of disappearing down an unintended 'rabbit hole' 
with this side-discussion (he says, with graceful under-statement).



The basic challenge came from my earlier (and blasé) repetition of the 
Python refrain "everything in Python is an object". Which led to:


<<<
For example, you may say "functions in Python are
objects", but you cannot put a function definition in the head of the
for loop clause.
>>>

Which is logical - to some degree, and in-isolation.

for def a_function( etc )... in iterable/iterator:

does not make sense. The 'head' (a more generic name, where Python says 
"target_list", that refines down to 'something which can identify the 
generated-value'.


So, no, there's an "everything" which (might be) an object but which 
cannot be used in that scenario.



Two "howevers":

However, instead of looking at the narrow clause, (third comment about 
wording not being taken as an whole!!!)* the full quotation was:


<<<
In Python, everything is an object. As long as the LHS is a legal-object 
which  makes sense for the situation, it can be used.

>>>

Context!

However, from the docs: "A function definition defines a user-defined 
function object (see section The standard type hierarchy)". Accordingly, 
is a function-definition an object? No! It defines an object.


That said, does anyone think that something like:

for a_function( etc ) in iterable/iterator:

is acceptable?
- see both Python definition and (full-)quotation.

I've not come-across a language which does allow such - YMMV/mea culpa; 
and am struggling to see how it could possibly be useful.


In-turn, how this discussion could become profitable...


* Looking at the correspondent's email-address (cf 'handle') - and as an 
unfair stereotype, raises the question of issues related to (English) 
language-skills - which, arrogantly implies/assumes that native 
English-speakers are all highly-capable. (?) A negative-interpretation 
is to note his apparent intelligence, but wonder if failing to represent 
others' comments fairly is deliberate, or carelessness. Is there an 
irony in behaving/failing in such, whilst attempting to hold Python's 
structure to some golden-ideal?



Web.Refs:
https://docs.python.org/3/reference/compound_stmts.html#the-for-statement
https://docs.python.org/3/reference/simple_stmts.html#grammar-token-python-grammar-target_list
https://docs.python.org/3/reference/compound_stmts.html#function-definitions

--
Regards,
=dn
--
https://mail.python.org/mailman/listinfo/python-list

Re: Extract lines from file, add to new files

[Left Right via Python-list]

> You said function. I made a function. You said "head of a for loop
> clause". I put it there. Problem was underspecified.

I also wrote a lot of letters, if you combine them very liberally,
without any regard to the order in which they were written or the
context in which they were used, you may come up with very surprising
findings.

> But if you're trying to tell me that a def statement should be a valid
> assignment target,

Why not just read what I wrote and work from there?  No, I didn't
write anything even remotely similar to this...  I don't want function
definition to be an assignment target.  I was giving an example of how
Python grammar works, how the rules govern what can or cannot be used
in a particular place...

In other words, if you aren't sure you understand the question, why
are you trying to reply to it? Is your goal to learn the meaning of
the question by giving arbitrary replies and hoping that the author of
the question restates it so that you understand it?  If so, I believe,
the better strategy would be to simply ask to restate the question.
Will save you the round-trip.

> You provided a way to create an anonymous function and that was not enough.
> I wonder if you could throw in the new := walrus operator to similarly make
> a named lambda function in a similar way.

The person you are replying to didn't understand the question and has
written something irrelevant.  It's not about being "enough".  I
honestly don't know why they are spending so much energy replying to
my messages :|

> Python grew and there was regular pressure to add keywords which might break
> existing programs. So, yes, sometimes, a keyword was re-used in a different
> context.

Why are keywords relevant to this?

> How often do you really think anyone out there NEEDS to define a function in
> the context mentioned?

This isn't about programmers writing programs that aren't about the
language.  It's about programmers who write language-related tools,
like linters, formatters etc.  I.e. the programmers who need to
consider any possible grammar product. And the reason I mentioned
function definition is, this, again: function definition is a
statement.  Python grammar rules prevent function definition from
appearing in left-hand side of the head of the for loop.  However, a
variable declaration, which is also a statement, is allowed there.
Programmers like grammar rules to be consistent, and it's surprising
if a particular larger context allows both statements and expressions.
I also explained why and how language authors would make a decision to
break this consistency: it saves some keystrokes for the programmers.
I.e. allows for shorter programs, while doesn't add any new abilities
to the language.
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

> Second time to ameliorate wording-dispute in this thread! The original
> phrase was: "[modified] BNF". Some of us have worked with various forms
> and evolutions of BNF since back in the days of COBOL-60 proposals, and
> know it when we see it!

OK, here are the conceptual differences between what Python grammar
language does and what you'd expect from anything that's based on BNF,
modified or not:

Python isn't a context-free language, so the grammar that is used to
describe it doesn't actually describe the language... so, it's a
"pretend grammar" that ignores indentation.  BNF is supposed to be
used to describe the language, it's not a "pretend" or "pseudo"
grammar, in a way we have at least two established grammar for
pseudo-code.

BNF and derivatives don't have an inherent mechanism for tiebreaks.
The mechanism is necessary because BNF rules can be tried in any
order.  Some grammar languages derived from BNF declare ambiguous
grammars invalid, some allow ambiguity, but say that the longest
prefix wins, and if there's still ambiguity after that, then such
grammar is invalid, some have special constructs to define "priority"
etc. My reading of Python grammar is that it works like PEG, where
rules are tried in the order they are defined.  This makes it less
expressive, but easier to work with.  This is, probably, the most
fundamental difference between the BNF family and the PEG family.

BNF and family languages rarely incorporate elements of Perl-like
regular expression parsing in the language (i.e. things like
lookaheads, lookbehinds etc.) This is more typical of the PEG family.

On top of this, the Python grammar language has a bunch of
"inventions" that are unique to it (I've never seen any other grammar
language use '.' in the same way Python uses it).  So, there's that
too.

Having worked with a bunch of different grammar languages, the one
used for Python isn't a recognizable BNF derivative.  I think the
authors used this as a description in the same way as today a lot of
programmers would use the word "IDE" to describe any text editor or
"REST" to describe any kind of server-client protocol over HTTP and so
on.  Or, how we'd use "Xerox" to name a copier machine, even if that
company didn't manufacture it, and even if the tech used for copying
is completely different.  And that's why I wrote that the grammar is
actually more like PEG, adding that it's neither, but seems to fall
more into that later category.

> Yes it is hard to read - and even harder to learn-from;

This wasn't my point.  My point is that it's hard to learn languages
that are "one off" in the group languages that all share a similar set
of rules. The difficulty comes from the surprise caused by the unique
use, not because there's something inherently difficult about reading
grammar languages.  In fact, however you look at Python's grammar
language, in a sense, it's a lot easier to read than Python itself
because it has significantly fewer rules.  Of course, the number of
rules doesn't entirely capture the difficulty, but it's a useful
metric.

> In Python, everything is an object. As long as the LHS is a legal-object
> which  makes sense for the situation, it can be used.

This is a very interesting statement... I don't think you are fully
aware of what it might mean :)  Here are just a few questions for you
to ponder:

* What is Python? Is it only Python 3.12?  Is Python 3.11 not Python?
How far back do you go to draw the line?
* What makes something an "object"? Is it the ability to dispatch on?
Is it the inheritance from "object" type?
* What elements of the language do you consider part of the language
that can be included in your "all" set.  Do types belong in that set?
Do expressions belong in that set?  What about comments?

Depending on how you answer these questions, you'd have some further
problems to deal with.  For example, historically, Python had plenty
of things that didn't inherit from "object" but acted similar to one.
I believe "module" objects were among the last to transition into
object inheritance lane, which might have happened some time around
Python 3.5.  Of course, there are plenty of things that are "in
Python", at least due to its grammar, that are hard to describe as
objects (eg. comments).  So, you'd have to make a special subset of
Python language that (eg. excludes comments) to claim that everything
is an object.

Most importantly, however, regardless of what you understand to be an
object, or how you decide to answer any of those questions: what value
does such a claim possibly have? Especially, given the context...

Furthermore, I'm absolutely convinced that what governs the
restrictions on the left-hand side isn't not whether it's understood
to be an object, but the grammar rules, that are unaware of the
concept of objects.  For example, you may say "functions in Python are
objects", but you cannot put a function definition in the head of the
for loop clause.
-- 

Re: Extract lines from file, add to new files

[dn via Python-list]

On 14/01/24 16:48, Chris Angelico wrote:

On Sun, 14 Jan 2024 at 14:43, dn via Python-list  wrote:

Similarly, whilst we could write:

a, b, c = 1, 2, 3



I would only do this when it aligns particularly well with the
algorithm being implemented. For example, you could start a Fibonacci
evaluator with "a, b = 0, 1". Otherwise, there's not all that much
reason to unpack three constants in this way.

(Though I am much more likely to use multiple initialization to set a
bunch of things to the SAME value, lilke "a = b = c = 0".)


Neatly stated!

--
Regards,
=dn

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Re: Extract lines from file, add to new files

[Left Right via Python-list]

> What do you mean?
>
> for x in lambda: ...:
>   ...
>
> Perfectly grammatical.

1. You put the lambda definition in the wrong place (it should be in
the left-hand side, or as Python calls it "star_targets", but you put
it into "star_expressions", which would be where the right-hand side
is drawn from).
2. You used what Python calls "lambdadef" in place of what Python
calls "function_def". I.e. lambda definition and function definition
are two different things, at least as far as grammar is considered.

So, you solved a different problem.
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

> What do you mean by this? Most languages I've worked with allow
> variables to be initialized with arbitrary expressions, and a lot of
> languages allow narrowly-scoped variables.

I'm talking about the *left* hand side of the assignment, not the
right hand side. Initialization with arbitrary expression -- arbitrary
expression is on the right. So, that's beside the point.

Here are examples of languages that don't have a feature analogous to
"augmented assignment target":

* Java
* C
* Shell

Examples of languages with limited use of destructuring:

* Haskell
* JavaScript
* Ruby
* Common Lisp

Examples of languages with a superset of destructuring:

* Prolog family of languages (in Prolog it's called "unification")

What is the problem with Python's "augmented assignment target"? -- It
is used in places where syntactically it is more common to introduce
variables (and in languages with the limited use of destructuring,
it's only possible to introduce variables in this context).  For
example, when destructuring an Array in JavaScript, the left-hand side
is restricted syntactically to a very small subset of the language
that, for example, excludes function application.  Typically, it's not
possible to use already defined variables in the left-hand side of the
variable definition, even if destructuring assignment is possible.
Prolog is the example of the opposite, where already defined variables
are allowed on both sides of unification, but Prolog doesn't have
function application in the same sense Python has, so it's still OK.

In general, in languages that aren't like Prolog, conceptually, it's
possible to either *define* variables (with optional initialization)
or to *reuse* them (in the context of assignment that usually looks
similar to initialization), but not both.  The fact that in Python you
can do both in the same place is surprising, eg. in the context of
loops.  Any language that distinguishes between expressions and
statements would have conceptual difficulties with allowing a mix in
the same context.  Typically, variable introduction is a statement in
such languages (as is the case in Python), so using an expression in
the same place as a variable introduction is strange.  To make this
shorter, Python allows:

for  in ... : ...

and

for  in ... : ...

which is unexpected, especially since the first form is a lot more
popular. Because the limited subset of expressions is desirable in
this context, many languages try to "cram" it into this box.  C, after
some standard iterations caved in and allowed statements in the
initialization component of the for loop (but only variable
declaration statements), for example. Other languages like JavaScript
developed a special subset of language for the purpose of describing
the relationship between multiple components of the object being
assigned as variables.

In every case, from the language development perspective, this looks
clumsy and unnecessary, as it is usually easy to write programs that
are exactly equivalent but don't require such workarounds. But, in
practice, programmers want to save a few keystrokes, and this pushes
the language authors to add such "features".  Python is furthermore
unique in how the workaround creates a lot of opportunities for abuse.

> The Python term, at least colloquially, is "tuple unpacking."

Well, why use colloquialism if there's a language specification? Also,
there weren't any tuples used in my example, at least not explicitly
(i could've been a tuple, but that wasn't specified).
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 08:15, Left Right  wrote:
> Python grammar rules prevent function definition from
> appearing in left-hand side of the head of the for loop.  However, a
> variable declaration, which is also a statement, is allowed there.

What is a "variable declaration" in Python? Please elaborate.

ChrisA
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

Chris,

It gets frustrating when people demand too much when strictly speaking, it
is not really needed or may cause new problems.

How often do you really think anyone out there NEEDS to define a function in
the context mentioned?

You provided a way to create an anonymous function and that was not enough.
I wonder if you could throw in the new := walrus operator to similarly make
a named lambda function in a similar way. 

And, in any case, you can make a function factory that returns a function
and call that function with appropriate arguments that might then create a
wide variety of functions by doing the def within.

Languages are tools and need not be the end-all for all people. You do not
want the language to get so complex that programmers do not have any idea
what valid code does. Consider the mess in multiple inheritance and trying
to figure out which of many classes will be the one where a method is
finally called using some diamond algorithm. It is both extremely powerful
but also silly to overuse such features.

Avi

-Original Message-
From: Python-list  On
Behalf Of Chris Angelico via Python-list
Sent: Sunday, January 14, 2024 8:34 AM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On Mon, 15 Jan 2024 at 00:27, Left Right  wrote:
>
> > What do you mean?
> >
> > for x in lambda: ...:
> >   ...
> >
> > Perfectly grammatical.
>
> 1. You put the lambda definition in the wrong place (it should be in
> the left-hand side, or as Python calls it "star_targets", but you put
> it into "star_expressions", which would be where the right-hand side
> is drawn from).
> 2. You used what Python calls "lambdadef" in place of what Python
> calls "function_def". I.e. lambda definition and function definition
> are two different things, at least as far as grammar is considered.
>
> So, you solved a different problem.

You said function. I made a function. You said "head of a for loop
clause". I put it there. Problem was underspecified.

But if you're trying to tell me that a def statement should be a valid
assignment target, I don't know what you're smoking, but I want you to
keep it a long way away from me. Can you name ANY language in which
that would make the slightest bit of sense?

ChrisA
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

It can be worth considering why a language is designed or altered in certain
ways to see if there was a tradeoff that made it seem worthwhile or easier
than some other choice.

Python grew and there was regular pressure to add keywords which might break
existing programs. So, yes, sometimes, a keyword was re-used in a different
context. And, yes, it was not originally conceived in a purely object
oriented context.

If you wanted to start over and built a new language very similar to python,
you might indeed make other choices now that seem more seamlessly to fit
together. You could set aside and reserve hundreds of keywords or some way
to extend keywords by insisting anything staring with "key_" cannot be used
in a variable name. You might design all the main objects supported to all
support a function that provides a length as well as every other method
needed so it looks purely object oriented.

But perhaps that would make it a tad harder to program it using other ways.
As an example, I can ask some sort program to order the results by the
length of items by passing it the function that does lengths as an argument.
If instead all we had was a method, that might be a bit different and
perhaps someone would simply make a tiny function that when called, invoked
the method.

So, we have a hybrid of sorts and have to live with it, warts and all, and
some of the warts may be seen by some as beauty marks.




-Original Message-
From: Python-list  On
Behalf Of Chris Angelico via Python-list
Sent: Sunday, January 14, 2024 7:32 AM
To: python-list@python.org
Subject: Re: Extract lines from file, add to new files

On Sun, 14 Jan 2024 at 23:28, Left Right  wrote:
> Having worked with a bunch of different grammar languages, the one
> used for Python isn't a recognizable BNF derivative.

That might possibly be because it isn't? It's not BNF. It's PEG. Or
are you a long way behind the times?

> For example, you may say "functions in Python are
> objects", but you cannot put a function definition in the head of the
> for loop clause.

What do you mean?

for x in lambda: ...:
   ...

Perfectly grammatical.

ChrisA
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Mon, 15 Jan 2024 at 00:27, Left Right  wrote:
>
> > What do you mean?
> >
> > for x in lambda: ...:
> >   ...
> >
> > Perfectly grammatical.
>
> 1. You put the lambda definition in the wrong place (it should be in
> the left-hand side, or as Python calls it "star_targets", but you put
> it into "star_expressions", which would be where the right-hand side
> is drawn from).
> 2. You used what Python calls "lambdadef" in place of what Python
> calls "function_def". I.e. lambda definition and function definition
> are two different things, at least as far as grammar is considered.
>
> So, you solved a different problem.

You said function. I made a function. You said "head of a for loop
clause". I put it there. Problem was underspecified.

But if you're trying to tell me that a def statement should be a valid
assignment target, I don't know what you're smoking, but I want you to
keep it a long way away from me. Can you name ANY language in which
that would make the slightest bit of sense?

ChrisA
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Sun, 14 Jan 2024 at 23:28, Left Right  wrote:
> Having worked with a bunch of different grammar languages, the one
> used for Python isn't a recognizable BNF derivative.

That might possibly be because it isn't? It's not BNF. It's PEG. Or
are you a long way behind the times?

> For example, you may say "functions in Python are
> objects", but you cannot put a function definition in the head of the
> for loop clause.

What do you mean?

for x in lambda: ...:
   ...

Perfectly grammatical.

ChrisA
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Sun, 14 Jan 2024 at 14:43, dn via Python-list  wrote:
> Similarly, whilst we could write:
>
> a, b, c = 1, 2, 3
>

I would only do this when it aligns particularly well with the
algorithm being implemented. For example, you could start a Fibonacci
evaluator with "a, b = 0, 1". Otherwise, there's not all that much
reason to unpack three constants in this way.

(Though I am much more likely to use multiple initialization to set a
bunch of things to the SAME value, lilke "a = b = c = 0".)
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Re: Extract lines from file, add to new files

[dn via Python-list]

On 13/01/24 00:11, Left Right via Python-list wrote:

To people discussing BNF:

The grammar language Python uses is *very* far from BNF. It's more
similar to PEG, but even then it's still quite far.  Python's grammar
is just its own thing, which makes it harder to read, if you are
already familiar with other more popular formats.


Second time to ameliorate wording-dispute in this thread! The original 
phrase was: "[modified] BNF". Some of us have worked with various forms 
and evolutions of BNF since back in the days of COBOL-60 proposals, and 
know it when we see it!


From the 'book of words': <>>

https://docs.python.org/3/reference/introduction.html#notation

Yes it is hard to read - and even harder to learn-from; which is why 
@Chris gave advice about preferring tutorials/text.


Just because there are other (more popular?) formats, doesn't make the 
one used here 'wrong'. In the same way that Python code differs from 
'the same' in other languages.


Putting it another way: if what Python is doing is wrong in your 
opinion, you are in the wrong place (for you).


That is not to say that Python has everything 'right'. One of my own 
bug-bears is very similar - that the string formatting 'mini-language' 
(https://docs.python.org/3/library/string.html#formatspec) does not 
follow the same rules about white-space as everything covered by the PEG 
Parser.


BTW the PEG Parser is relatively new to Python. IIRC there was comment 
at the time of its first application, that some 'other' areas of Python 
might take a while to be converted-over.




I've also found bugs in Python parser before, so had this turned out


Sorry, didn't recognise your email-handle - not that I'm a Python 
Core-Dev, and pretty much ignore the "Ideas" list these days. Must have 
missed your previous contributions...




to be a real issue, this wouldn't have been the first time.  There are
plenty of weird corners in Python grammar that allow unexpected
programs to parse (and sometimes even run!), and these are very often
connected to assignments, because, in general, assignments in Python
are very elaborate and hard to describe / conceptualize about.  The
most popular example I've even seen used in coding interviews (which I
think is a silly gimmick, but that's kind of the whole point of a lot
of these interviews...) is:

 x = [...]
 for x[i] in x: print(i)

Which is not an assignment by itself, but the "weirdness" results from
the loop syntax sharing definitions with the "destructuring bind"
style of assignment (i.e. where the left-hand side can be an arbitrary
complex expression).


You're right. (also about stupid 'interviewing' ideas) If someone asked 
me this, I'd respond by asking if that was the standard of code they 
work towards - and depending upon that answer would either walk-out or 
refer the matter to a more senior manager!



In Python, everything is an object. As long as the LHS is a legal-object 
which  makes sense for the situation, it can be used.


Also, an identifier (whether x, i, or x[ i ]) should not only be 
considered to be its own object, but is best regarded as a pointer to 
some value. This is how we can have an 'immutable' tuple 'containing' a 
mutable list (for example) - such that elements of that list may be 
changed, despite being 'part of' an immutable construct!


Programs are read by people. If something is a "weirdness", then 
chances-are it won't survive a CodeReview/a professional team's 
expected-standard. Not limited to Python-code!




I was surprised, for example, to learn that "as" in "with_stmt" isn't
shared with "as" in "except_block" (so, from the grammar perspective,
these are two different keywords), and that asterisk in "except_block"
isn't shared with "star_target" (also weird, since you'd think these
should be the same thing).  In general, and by and large, if you look
at Python's grammar there are many "weird" choices that it makes to
describe the language which seem counterintuitive to the programmer
who tries to learn the language from examples (i.e. context-depending
meaning of parenthesis, of asterisk, of period etc.)  Having been
exposed to this, you'd start to expect that some of this weirdness
will eventually result in bugs, or at least in unexpected behavior.


You're right. It is potentially confusing when the same word/symbol is 
used in different contexts.


I've heard similar questions from learners, but not had anyone trying to 
mis-use something extrapolating from how the 'same' is used elsewhere. YMMV!


It's the context part that's important to remember. If someone calls you 
"mate", that has different connotations depending upon whether you're 
friends, you're on a Navy ship, or in a more intimate situation - indeed 
there are some cultures in which the word "mate" is not used to mean 
'friend' at all. Which is (more) right? Which wrong?


Perhaps you're aiming for, or even used to, a more 

Re: Extract lines from file, add to new files

[dn via Python-list]

On 12/01/24 08:53, Rich Shepard via Python-list wrote:

On Thu, 11 Jan 2024, Piergiorgio Sartor via Python-list wrote:


Why not to use bash script for all?


Piergiorgio,

That's certainly a possibility, and may well be better than python for this
task.


(sitting in a meeting with little to occupy my mind, whilst tidying 
email-InBox came back to this conversation)



In the bare-description of the task, I might agree to sticking with 
BASH. The OP did say that the output from this will become input to a 
sed/mailx task!

(we trust, does not involve spamming innocent folk)

However, that task could also be accomplished in Python. So, unless 
there is an existing script (perhaps) quite why one would choose to do 
half in Python and half in BASH (or...) is a question.



Because this is a Python forum, do the whole thing in one mode - our mode!

Previous suggestions involved identifying a line by its content.

Could use a neat state-transition solution.

However, there is no need to consider the input-data as lines because of 
the concept of "white-space", well-utilised by some of Python's built-in 
string-functions. See code-sample, below.


As mentioned before, the idea of splitting the one file (data-items 
related by serial-progression) and creating two quite-separate 
data-constructs (in this case: one holding the person's name in one file 
and the other the person's email-address in another) which are related 
'across', ie line-by-line, is an architectural error?horror. Such would 
be hard to maintain, and over-time impossible to guarantee integrity. 
Assuming this is not a one-off exercise, see elsewhere for advice to 
store the captured data in some more-useful format, eg JSON, CSV, or 
even put into a MongoDB or RDBMS.



** code

""" PythonExperiments:rich.py
Demonstrate string extraction.
"""

__author__ = "dn, IT Consultant"
__python__ = "3.12"
__created__ = "PyCharm, 14 Jan 2024"
__copyright__ = "Copyright © 2024~"
__license__ = "GNU General Public License v3.0"

# PSL
import more_itertools as it

DATA_FILE = "rich_data_file"
READ_ONLY = "r"
AS_PAIRS = 2
STRICT_PAIRING = True


if __name__ == "__main__":
print("\nCommencing execution\n")

with open( DATA_FILE, READ_ONLY, ) as df:
data = df.read()

data_as_list = data.split()
paired_data = it.chunked( data_as_list, AS_PAIRS, STRICT_PAIRING, )

for name, email_address in paired_data:
# replace this with email-function
# and/or with storage-function
print( name, email_address, )

print("\nTerminating")

** sample output

Calvin cal...@example.com
Hobbs ho...@some.com
...

**

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Regards,
=dn
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 13/01/24 3:14 pm, Chris Angelico wrote:

On Sat, 13 Jan 2024 at 13:11, Left Right via Python-list
 wrote:


  Very few
languages allow arbitrary complex expressions in the same place they
allow variable introduction.


What do you mean by this? Most languages I've worked with allow
variables to be initialized with arbitrary expressions, and a lot of
languages allow narrowly-scoped variables.


I think he means that in some languages the for-loop target serves as
the declaration of a new variable, and as such has to be a bare name.

Python isn't like that -- the target of a for-statement is treated
exactly the same way as the lhs of an assignment. It's not scoped to the
loop.

BTW, the equivalent thing is valid in C too, so anyone familiar with C
is unlikely to be surprised by this either.

#include 

int x[10];
int i;

int main() {
  i = 5;
  for (x[i] = 0; x[i] < 10; x[i]++)
printf("%d\n", x[i]);
}

Output:

0
1
2
3
4
5
6
7
8
9

--
Greg
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 13/01/24 1:45 pm, Left Right wrote:


I use the term "destructuring" in the same way Hyperspec uses it.
It's not a Python term.  I don't know what you call the same thing in
Python.  I'm not sure what you understand from it.


I thought you meant what is usually called "unpacking" in Python. I
don't know anything about Hyperspec, so I don't know what it means
there.

The fact that i was being printed inside the loop made me think
that some deeper level of surprise was being intended, such as
the value of i somehow getting changed by the assignment.

--
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Re: Extract lines from file, add to new files

[Dan Sommers via Python-list]

On 2024-01-13 at 11:34:29 +0100,
Left Right  wrote:

> > The Python term, at least colloquially, is "tuple unpacking."

That quote is from me.  Please do preserve attributions.

> Well, why use colloquialism if there's a language specification? Also,
> there weren't any tuples used in my example, at least not explicitly
> (i could've been a tuple, but that wasn't specified).

According to the language specification,⁰ it's a "target list," and
there can be more than one target in that list.

The unpacking isn't really called anything, it's just the way Python
assignment works, all the way back to its earliest stages.¹

⁰ https://docs.python.org/3/reference/simple_stmts.html#assignment-statements,
¹ https://docs.python.org/release/1.4/ref/ref6.html#HDR2
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Re: Extract lines from file, add to new files

[Dan Sommers via Python-list]

On 2024-01-13 at 02:02:39 +0100,
Left Right via Python-list  wrote:

> Actually, after some Web search.  I think, based on this:
> https://docs.python.org/3/reference/simple_stmts.html#grammar-token-python-grammar-augtarget
> that in Python you call this "augmented assignment target". The term
> isn't in the glossary, but so are many others.

The Python term, at least colloquially, is "tuple unpacking."

HTH.
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Sat, 13 Jan 2024 at 13:11, Left Right via Python-list
 wrote:
>
>  Very few
> languages allow arbitrary complex expressions in the same place they
> allow variable introduction.

What do you mean by this? Most languages I've worked with allow
variables to be initialized with arbitrary expressions, and a lot of
languages allow narrowly-scoped variables.

ChrisA
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

Actually, after some Web search.  I think, based on this:
https://docs.python.org/3/reference/simple_stmts.html#grammar-token-python-grammar-augtarget
that in Python you call this "augmented assignment target". The term
isn't in the glossary, but so are many others.

On Sat, Jan 13, 2024 at 1:45 AM Left Right  wrote:
>
> > surprising for me:
>
> Surprise is subjective, it's based on personal experience. Very few
> languages allow arbitrary complex expressions in the same place they
> allow variable introduction. The fact that "i" is not defined is
> irrelevant to this example.  Most programmers who haven't memorized
> Python grammar by heart, but expect the language to behave similar to
> the languages in the same category would be surprised this code is
> valid (i.e. can be parsed), whether it results in error or not is of
> no consequence.
>
> > There's no destructuring going on here
>
> I use the term "destructuring" in the same way Hyperspec uses it.
> It's not a Python term.  I don't know what you call the same thing in
> Python.  I'm not sure what you understand from it.
>
> On Sat, Jan 13, 2024 at 12:37 AM Greg Ewing via Python-list
>  wrote:
> >
> > On 13/01/24 12:11 am, Left Right wrote:
> > >  x = [...]
> > >  for x[i] in x: print(i)
> >
> > I suspect you've misremembered something, because this doesn't
> > do anything surprising for me:
> >
> >  >>> x = [1, 2, 3]
> >  >>> for x[i] in x: print(i)
> > ...
> > Traceback (most recent call last):
> >File "", line 1, in 
> > NameError: name 'i' is not defined
> >
> > There's no destructuring going on here, just assignment to a
> > sequence item.
> >
> > --
> > Greg
> > --
> > https://mail.python.org/mailman/listinfo/python-list
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

> surprising for me:

Surprise is subjective, it's based on personal experience. Very few
languages allow arbitrary complex expressions in the same place they
allow variable introduction. The fact that "i" is not defined is
irrelevant to this example.  Most programmers who haven't memorized
Python grammar by heart, but expect the language to behave similar to
the languages in the same category would be surprised this code is
valid (i.e. can be parsed), whether it results in error or not is of
no consequence.

> There's no destructuring going on here

I use the term "destructuring" in the same way Hyperspec uses it.
It's not a Python term.  I don't know what you call the same thing in
Python.  I'm not sure what you understand from it.

On Sat, Jan 13, 2024 at 12:37 AM Greg Ewing via Python-list
 wrote:
>
> On 13/01/24 12:11 am, Left Right wrote:
> >  x = [...]
> >  for x[i] in x: print(i)
>
> I suspect you've misremembered something, because this doesn't
> do anything surprising for me:
>
>  >>> x = [1, 2, 3]
>  >>> for x[i] in x: print(i)
> ...
> Traceback (most recent call last):
>File "", line 1, in 
> NameError: name 'i' is not defined
>
> There's no destructuring going on here, just assignment to a
> sequence item.
>
> --
> Greg
> --
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Re: Extract lines from file, add to new files

[Greg Ewing via Python-list]

On 13/01/24 12:11 am, Left Right wrote:

 x = [...]
 for x[i] in x: print(i)


I suspect you've misremembered something, because this doesn't
do anything surprising for me:

>>> x = [1, 2, 3]
>>> for x[i] in x: print(i)
...
Traceback (most recent call last):
  File "", line 1, in 
NameError: name 'i' is not defined

There's no destructuring going on here, just assignment to a
sequence item.

--
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

To people discussing BNF:

The grammar language Python uses is *very* far from BNF. It's more
similar to PEG, but even then it's still quite far.  Python's grammar
is just its own thing, which makes it harder to read, if you are
already familiar with other more popular formats.

I've also found bugs in Python parser before, so had this turned out
to be a real issue, this wouldn't have been the first time.  There are
plenty of weird corners in Python grammar that allow unexpected
programs to parse (and sometimes even run!), and these are very often
connected to assignments, because, in general, assignments in Python
are very elaborate and hard to describe / conceptualize about.  The
most popular example I've even seen used in coding interviews (which I
think is a silly gimmick, but that's kind of the whole point of a lot
of these interviews...) is:

x = [...]
for x[i] in x: print(i)

Which is not an assignment by itself, but the "weirdness" results from
the loop syntax sharing definitions with the "destructuring bind"
style of assignment (i.e. where the left-hand side can be an arbitrary
complex expression).

I was surprised, for example, to learn that "as" in "with_stmt" isn't
shared with "as" in "except_block" (so, from the grammar perspective,
these are two different keywords), and that asterisk in "except_block"
isn't shared with "star_target" (also weird, since you'd think these
should be the same thing).  In general, and by and large, if you look
at Python's grammar there are many "weird" choices that it makes to
describe the language which seem counterintuitive to the programmer
who tries to learn the language from examples (i.e. context-depending
meaning of parenthesis, of asterisk, of period etc.)  Having been
exposed to this, you'd start to expect that some of this weirdness
will eventually result in bugs, or at least in unexpected behavior.



Anyways. To the OP: I'm sorry to hijack your question. Below is the
complete program:

with (
open('example.txt', 'r') as e,
open('emails.txt', 'w') as m,
open('salutations.txt', 'w') as s,
):
for line in e:
if line.strip():
(m if '@' in line else s).write(line)

it turned out to be not quite the golfing material I was hoping for.
But, perhaps a somewhat interesting aspect of this program you don't
see used a lot in the wild is the parenthesis in the "with" head.  So,
it's not a total write-off from the learning perspective.  I.e. w/o
looking at the grammar, and had I have this code in a coding interview
question, I wouldn't be quite sure whether this code would work or
not: one way to interpret what's going on here is to think that the
expression inside parentheses is a tuple, and since tuples aren't
context managers, it wouldn't have worked (or maybe not even parsed as
"as" wouldn't be allowed inside tuple definition since there's no
"universal as-expression" in Python it's hard to tell what the rules
are).  But, it turns out there's a form of "with" that has parentheses
for decoration purposes, and that's why it parses and works to the
desired effect.

Since it looks like you are doing this for educational reasons, I
think there's a tiny bit of value to my effort.

On Fri, Jan 12, 2024 at 8:08 AM Grizzy Adams via Python-list
 wrote:
>
> Thursday, January 11, 2024  at 10:44, Rich Shepard via Python-list wrote:
> Re: Extract lines from file, add to (at least in part)
>
> >On Thu, 11 Jan 2024, MRAB via Python-list wrote:
>
> >> From the look of it:
> >> 1. If the line is empty, ignore it.
> >> 2. If the line contains "@", it's an email address.
> >> 3. Otherwise, it's a name.
>
> If that is it all? a simple Grep would do (and save on the blank line)
> --
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RE: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Fri, 12 Jan 2024, AVI GROSS via Python-list wrote:


But is the solution a good one for some purpose? The two output files may
end up being out of sync for all kinds of reasons. One of many "errors"
can happen if multiple lines in a row do not have an "@" or a person's
name does, for example. What if someone supplied more than one email
address with a comma separator? This may not be expected but could cause
problems.


Avi,

For my use 1) the salutation and email address (always with an '@') are
sequential and 2) I'm developing the script to extract both from the same
file.

Regards,

Rich
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RE: Extract lines from file, add to new files

[AVI GROSS via Python-list]

If the data in the input file is exactly as described and consists of
alternating lines containing a name and email address, or perhaps an
optional blank line, then many solutions are possible using many tools
including python programs.

But is the solution a good one for some purpose? The two output files may
end up being out of sync for all kinds of reasons. One of many "errors" can
happen if multiple lines in a row do not have an "@" or a person's name
does, for example. What if someone supplied more than one email address with
a comma separator? This may not be expected but could cause problems.

Some of the other tools mentioned would not care and produce garbage. Grep
as an example could be run twice asking for lines with an "@" and then lines
without. In this case, that would be trivial. Blank lines, or ones with just
whitespace, might need another pass to be omitted.

But a real challenge would be to parse the file in a language like Python
and find all VALID stretches in the data and construct a data structure
containing either a valid name or something specific like "ANONYMOUS"
alongside an email address. These may be written out as soon as it is
considered valid, or collected in something like a list. You can do further
processing if you want the results in some order or remove duplicates or bad
email addresses and so on. In that scenario, the two files would be written
out at the end.

Python can do the above while some of the other tools mentioned are not
really designed for it. Further, many of the tools are not generally
available everywhere.

Another question is why it makes sense to produce two output files to
contain the data that may not be linked and would not be easy to edit and
keep synchronized such as to remove or add entries. There are many ways to
save the data that might be more robust for many purposes. It looks like the
application intended is a sort of form letter merge where individual emails
will be sent that contain a personalized greeting. Unless that application
has already been written, there are many other ways that make sense. One
obvious one is to save the data in a databases as columns in a table. Other
ones are to write one file with entries easily parsed out such as:

NAME: name | EMAIL: email

Whatever the exact design, receiving software could parse that out as needed
by the simpler act of reading one line at a time.

And, of course, there are endless storage formats such as a CSV file or
serializing your list of objects to a file so that the next program can load
them in and operate from memory on all the ones it wants. The two file
solution may seem simpler but harks back to how some computing was done in
early days when list of objects might be handled by having multiple arrays
with each containing one aspect of the object and updating required
rememebreing to touch each array the same way.. That can still be a useful
technique when some operations being done in a vectoried manner might be
faster than an array of objects, but is more often a sign of poor code.






-Original Message-
From: Python-list  On
Behalf Of Grizzy Adams via Python-list
Sent: Friday, January 12, 2024 1:59 AM
To: Rich Shepard via Python-list ; Rich Shepard

Subject: Re: Extract lines from file, add to new files

Thursday, January 11, 2024  at 10:44, Rich Shepard via Python-list wrote:
Re: Extract lines from file, add to (at least in part)

>On Thu, 11 Jan 2024, MRAB via Python-list wrote:

>> From the look of it:
>> 1. If the line is empty, ignore it.
>> 2. If the line contains "@", it's an email address.
>> 3. Otherwise, it's a name.

If that is it all? a simple Grep would do (and save on the blank line)
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Re: Extract lines from file, add to new files

[Grizzy Adams via Python-list]

Thursday, January 11, 2024  at 10:44, Rich Shepard via Python-list wrote:
Re: Extract lines from file, add to (at least in part)

>On Thu, 11 Jan 2024, MRAB via Python-list wrote:

>> From the look of it:
>> 1. If the line is empty, ignore it.
>> 2. If the line contains "@", it's an email address.
>> 3. Otherwise, it's a name.

If that is it all? a simple Grep would do (and save on the blank line)
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Re: Extract lines from file, add to new files

[dn via Python-list]

On 12/01/24 12:56, Chris Angelico via Python-list wrote:

On Fri, 12 Jan 2024 at 08:56, Left Right via Python-list
 wrote:


By the way, in an attempt to golf this problem, I discovered this,
which seems like a parser problem:


When you jump immediately to "this is a bug", all you do is make


"seems"!

but yes, it is a (much) less-likely explanation.



yourself look like an idiot. Unsurprisingly, this is NOT a bug, this
is simply that you didn't understand what was going on. The grammar
isn't easy to read, and it's usually better to read the documentation
instead.


Those of us who studied Computer Science may well have been 
taught/expected to learn how to read [modified] BNF - indeed to have 
worked in that (cf coding in Python).


Accordingly, the English text is likely easier to understand, but 
sometimes the BNF offers finer-detail or can be used to clarify some 
mis- or insufficiently-understood aspect of the text. IMHO/YMMV/etc...




(Plus, golfing isn't really a goal in Python, and you didn't  shorten
the code by much at all. Good job.)


I took my hat off to the poster, being prepared to dive-in and do this. 
Accordingly, was more than happy to help set him/her back onto 'the 
straight and narrow'.


(yes it was a BNF-failing - which, credit where credit's due, I think 
was realised at the same time as response was typed)


How many others just want us to do all their thinking for them?
(there's a rude comment about wiping noses - but probably a step too far 
wrt the CoC)


--
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=dn
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Re: Extract lines from file, add to new files

[Chris Angelico via Python-list]

On Fri, 12 Jan 2024 at 08:56, Left Right via Python-list
 wrote:
>
> By the way, in an attempt to golf this problem, I discovered this,
> which seems like a parser problem:

When you jump immediately to "this is a bug", all you do is make
yourself look like an idiot. Unsurprisingly, this is NOT a bug, this
is simply that you didn't understand what was going on. The grammar
isn't easy to read, and it's usually better to read the documentation
instead.

(Plus, golfing isn't really a goal in Python, and you didn't  shorten
the code by much at all. Good job.)

ChrisA
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Re: Extract lines from file, add to new files

[dn via Python-list]

On 12/01/24 10:33, Left Right via Python-list wrote:

By the way, in an attempt to golf this problem, I discovered this,
which seems like a parser problem:

This is what Python tells me about its grammar:

with_stmt:
 | 'with' '(' ','.with_item+ ','? ')' ':' block
 | 'with' ','.with_item+ ':' [TYPE_COMMENT] block
 | ASYNC 'with' '(' ','.with_item+ ','? ')' ':' block
 | ASYNC 'with' ','.with_item+ ':' [TYPE_COMMENT] block

with_item:
 | expression 'as' star_target &(',' | ')' | ':')
 | expression

 From which I figured why not something like this:

with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
 for line in e:
 if line.strip():
 (m if '@' in line else s).write(line)

Which, surprise, parsers! But it seems like it's parse is wrong,
because running this I get:

❯ python ./split_emails.py
Traceback (most recent call last):
   File "/home/?/doodles/python/./split_emails.py", line 1, in 
 with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
TypeError: 'tuple' object does not support the context manager protocol

It seems to me it shouldn't have been parsed as a tuple. The
parenthesis should've been interpreted just as a decoration.

NB. I'm using 3.11.6.
A series of comma-separated items will be parsed as a tuple (some people 
think it is bounding-parentheses which define).


In this case, the issue is 'connecting' the context-manager "expression" 
with its (as) "target". These should be more-closely paired:-


with ( open( 'example.txt', 'r', ) as e,
   open( 'emails.txt', 'w', ) as m,
   open( 'salutations.txt', 'w', ) as s
   ):

(NB code not executed here)


A data-architecture of having related-data in separated serial-files is 
NOT recommendable!


--
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=dn
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

Ah, nevermind. I need to be more careful, there isn't an "'as'
star_target" after the first rule.

On Thu, Jan 11, 2024 at 10:33 PM Left Right  wrote:
>
> By the way, in an attempt to golf this problem, I discovered this,
> which seems like a parser problem:
>
> This is what Python tells me about its grammar:
>
> with_stmt:
> | 'with' '(' ','.with_item+ ','? ')' ':' block
> | 'with' ','.with_item+ ':' [TYPE_COMMENT] block
> | ASYNC 'with' '(' ','.with_item+ ','? ')' ':' block
> | ASYNC 'with' ','.with_item+ ':' [TYPE_COMMENT] block
>
> with_item:
> | expression 'as' star_target &(',' | ')' | ':')
> | expression
>
> From which I figured why not something like this:
>
> with (open('example.txt', 'r'), open('emails.txt', 'w'),
> open('salutations.txt', 'w')) as e, m, s:
> for line in e:
> if line.strip():
> (m if '@' in line else s).write(line)
>
> Which, surprise, parsers! But it seems like it's parse is wrong,
> because running this I get:
>
> ❯ python ./split_emails.py
> Traceback (most recent call last):
>   File "/home/?/doodles/python/./split_emails.py", line 1, in 
> with (open('example.txt', 'r'), open('emails.txt', 'w'),
> open('salutations.txt', 'w')) as e, m, s:
> TypeError: 'tuple' object does not support the context manager protocol
>
> It seems to me it shouldn't have been parsed as a tuple. The
> parenthesis should've been interpreted just as a decoration.
>
> NB. I'm using 3.11.6.
>
> On Thu, Jan 11, 2024 at 10:20 PM Thomas Passin via Python-list
>  wrote:
> >
> > On 1/11/2024 1:27 PM, MRAB via Python-list wrote:
> > > On 2024-01-11 18:08, Rich Shepard via Python-list wrote:
> > >> It's been several years since I've needed to write a python script so I'm
> > >> asking for advice to get me started with a brief script to separate names
> > >> and email addresses in one file into two separate files:
> > >> salutation.txt and
> > >> emails.txt.
> > >>
> > >> An example of the input file:
> > >>
> > >> Calvin
> > >> cal...@example.com
> > >>
> > >> Hobbs
> > >> ho...@some.com
> > >>
> > >> Nancy
> > >> na...@herown.com
> > >>
> > >> Sluggo
> > >> slu...@another.com
> > >>
> > >> Having extracted salutations and addresses I'll write a bash script using
> > >> sed and mailx to associate a message file with each name and email
> > >> address.
> > >>
> > >> I'm unsure where to start given my lack of recent experience.
> > >>
> > >  From the look of it:
> > >
> > > 1. If the line is empty, ignore it.
> > >
> > > 2. If the line contains "@", it's an email address.
> > >
> > > 3. Otherwise, it's a name.
> >
> > You could think about a single Python script that looks through your
> > input file and constructs all the message files without ever writing
> > separate salutation and address files at all.  Then you wouldn't need to
> > write the sed and mailx scripts.  It shouldn't be much harder than
> > peeling out the names and addresses into separate files.
> >
> > If you haven't written any Python for some years, the preferred way to
> > read and write files is using a "with" statement, like this:
> >
> > with open('email_file.txt', encoding = 'utf-8') as f:
> >  lines = f.readlines()
> >  for line in lines:
> >  if not line.strip():  # Skip blank lines
> >  continue
> >  # Do something with this line
> >
> > You don't need to close the file because when the "with" block ends the
> > file will be closed for you.
> >
> > If the encoding is not utf-8 and you know what it will be, use that
> > encoding instead.
> >
> > --
> > https://mail.python.org/mailman/listinfo/python-list
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Re: Extract lines from file, add to new files

[Left Right via Python-list]

By the way, in an attempt to golf this problem, I discovered this,
which seems like a parser problem:

This is what Python tells me about its grammar:

with_stmt:
| 'with' '(' ','.with_item+ ','? ')' ':' block
| 'with' ','.with_item+ ':' [TYPE_COMMENT] block
| ASYNC 'with' '(' ','.with_item+ ','? ')' ':' block
| ASYNC 'with' ','.with_item+ ':' [TYPE_COMMENT] block

with_item:
| expression 'as' star_target &(',' | ')' | ':')
| expression

From which I figured why not something like this:

with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
for line in e:
if line.strip():
(m if '@' in line else s).write(line)

Which, surprise, parsers! But it seems like it's parse is wrong,
because running this I get:

❯ python ./split_emails.py
Traceback (most recent call last):
  File "/home/?/doodles/python/./split_emails.py", line 1, in 
with (open('example.txt', 'r'), open('emails.txt', 'w'),
open('salutations.txt', 'w')) as e, m, s:
TypeError: 'tuple' object does not support the context manager protocol

It seems to me it shouldn't have been parsed as a tuple. The
parenthesis should've been interpreted just as a decoration.

NB. I'm using 3.11.6.

On Thu, Jan 11, 2024 at 10:20 PM Thomas Passin via Python-list
 wrote:
>
> On 1/11/2024 1:27 PM, MRAB via Python-list wrote:
> > On 2024-01-11 18:08, Rich Shepard via Python-list wrote:
> >> It's been several years since I've needed to write a python script so I'm
> >> asking for advice to get me started with a brief script to separate names
> >> and email addresses in one file into two separate files:
> >> salutation.txt and
> >> emails.txt.
> >>
> >> An example of the input file:
> >>
> >> Calvin
> >> cal...@example.com
> >>
> >> Hobbs
> >> ho...@some.com
> >>
> >> Nancy
> >> na...@herown.com
> >>
> >> Sluggo
> >> slu...@another.com
> >>
> >> Having extracted salutations and addresses I'll write a bash script using
> >> sed and mailx to associate a message file with each name and email
> >> address.
> >>
> >> I'm unsure where to start given my lack of recent experience.
> >>
> >  From the look of it:
> >
> > 1. If the line is empty, ignore it.
> >
> > 2. If the line contains "@", it's an email address.
> >
> > 3. Otherwise, it's a name.
>
> You could think about a single Python script that looks through your
> input file and constructs all the message files without ever writing
> separate salutation and address files at all.  Then you wouldn't need to
> write the sed and mailx scripts.  It shouldn't be much harder than
> peeling out the names and addresses into separate files.
>
> If you haven't written any Python for some years, the preferred way to
> read and write files is using a "with" statement, like this:
>
> with open('email_file.txt', encoding = 'utf-8') as f:
>  lines = f.readlines()
>  for line in lines:
>  if not line.strip():  # Skip blank lines
>  continue
>  # Do something with this line
>
> You don't need to close the file because when the "with" block ends the
> file will be closed for you.
>
> If the encoding is not utf-8 and you know what it will be, use that
> encoding instead.
>
> --
> https://mail.python.org/mailman/listinfo/python-list
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Re: Extract lines from file, add to new files

[Thomas Passin via Python-list]

On 1/11/2024 1:27 PM, MRAB via Python-list wrote:

On 2024-01-11 18:08, Rich Shepard via Python-list wrote:

It's been several years since I've needed to write a python script so I'm
asking for advice to get me started with a brief script to separate names
and email addresses in one file into two separate files: 
salutation.txt and

emails.txt.

An example of the input file:

Calvin
cal...@example.com

Hobbs
ho...@some.com

Nancy
na...@herown.com

Sluggo
slu...@another.com

Having extracted salutations and addresses I'll write a bash script using
sed and mailx to associate a message file with each name and email 
address.


I'm unsure where to start given my lack of recent experience.


 From the look of it:

1. If the line is empty, ignore it.

2. If the line contains "@", it's an email address.

3. Otherwise, it's a name.


You could think about a single Python script that looks through your 
input file and constructs all the message files without ever writing 
separate salutation and address files at all.  Then you wouldn't need to 
write the sed and mailx scripts.  It shouldn't be much harder than 
peeling out the names and addresses into separate files.


If you haven't written any Python for some years, the preferred way to 
read and write files is using a "with" statement, like this:


with open('email_file.txt', encoding = 'utf-8') as f:
lines = f.readlines()
for line in lines:
if not line.strip():  # Skip blank lines
continue
# Do something with this line

You don't need to close the file because when the "with" block ends the 
file will be closed for you.


If the encoding is not utf-8 and you know what it will be, use that 
encoding instead.


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Re: Extract lines from file, add to new files

[Mirko via Python-list]

Am 11.01.24 um 20:53 schrieb Rich Shepard via Python-list:

On Thu, 11 Jan 2024, Piergiorgio Sartor via Python-list wrote:


Why not to use bash script for all?


Piergiorgio,

That's certainly a possibility, and may well be better than python 
for this

task.

Thank you,

Rich


awk '/@/ {print >>"emails.txt";next};NF{print >>"salutation.txt"}' 
input.txt



SCNR ;-)
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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Thu, 11 Jan 2024, Piergiorgio Sartor via Python-list wrote:


Why not to use bash script for all?


Piergiorgio,

That's certainly a possibility, and may well be better than python for this
task.

Thank you,

Rich
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Re: Extract lines from file, add to new files

[Piergiorgio Sartor via Python-list]

On 11/01/2024 19.08, Rich Shepard wrote:

It's been several years since I've needed to write a python script so I'm
asking for advice to get me started with a brief script to separate names
and email addresses in one file into two separate files: salutation.txt and
emails.txt.

An example of the input file:

Calvin
cal...@example.com

Hobbs
ho...@some.com

Nancy
na...@herown.com

Sluggo
slu...@another.com

Having extracted salutations and addresses I'll write a bash script using
sed and mailx to associate a message file with each name and email address.


Why not to use bash script for all?

bye,

--

piergiorgio

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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Thu, 11 Jan 2024, Mats Wichmann via Python-list wrote:


4. Don't assume it's going to be "plain text" if the email info is
harvested from external sources (like incoming emails) - you'll end up
stumbling over a 誰かのユーザー from somewhere. Process as bytes, or be
really careful about which encodings you allow - which for email "names"
is something you can't actually control.


Mats,

Not an issue for me.

Regards,

Rich
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Re: Extract lines from file, add to new files

[Mats Wichmann via Python-list]

On 1/11/24 11:27, MRAB via Python-list wrote:

On 2024-01-11 18:08, Rich Shepard via Python-list wrote:

It's been several years since I've needed to write a python script so I'm
asking for advice to get me started with a brief script to separate names
and email addresses in one file into two separate files: 
salutation.txt and

emails.txt.

An example of the input file:

Calvin
cal...@example.com

Hobbs
ho...@some.com

Nancy
na...@herown.com

Sluggo
slu...@another.com

Having extracted salutations and addresses I'll write a bash script using
sed and mailx to associate a message file with each name and email 
address.


I'm unsure where to start given my lack of recent experience.


 From the look of it:

1. If the line is empty, ignore it.

2. If the line contains "@", it's an email address.

3. Otherwise, it's a name.



4. Don't assume it's going to be "plain text" if the email info is 
harvested from external sources (like incoming emails) - you'll end up 
stumbling over a 誰かのユーザー from somewhere.  Process as bytes, or be really 
careful about which encodings you allow - which for email "names" is 
something you can't actually control.


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Re: Extract lines from file, add to new files

[Rich Shepard via Python-list]

On Thu, 11 Jan 2024, MRAB via Python-list wrote:


From the look of it:
1. If the line is empty, ignore it.
2. If the line contains "@", it's an email address.
3. Otherwise, it's a name.


MRAB,

Thanks. I'll take it from here.

Regards,

Rich
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Re: Extract lines from file, add to new files

[MRAB via Python-list]

On 2024-01-11 18:08, Rich Shepard via Python-list wrote:

It's been several years since I've needed to write a python script so I'm
asking for advice to get me started with a brief script to separate names
and email addresses in one file into two separate files: salutation.txt and
emails.txt.

An example of the input file:

Calvin
cal...@example.com

Hobbs
ho...@some.com

Nancy
na...@herown.com

Sluggo
slu...@another.com

Having extracted salutations and addresses I'll write a bash script using
sed and mailx to associate a message file with each name and email address.

I'm unsure where to start given my lack of recent experience.


From the look of it:

1. If the line is empty, ignore it.

2. If the line contains "@", it's an email address.

3. Otherwise, it's a name.

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