Re: Asynchronous processing is more efficient -- surely not?

[Paul Rudin]

Steven D'Aprano  writes:

> So, I'm, still trying to wrap my brain around async processing, and I 
> started reading this tutorial:
>
> http://stackabuse.com/python-async-await-tutorial/
>
> and the very first paragraph broke my brain.
>
> "Asynchronous programming has been gaining a lot of traction in the past 
> few years, and for good reason. Although it can be more difficult than 
> the traditional linear style, it is also much more efficient."
>
> I can agree with the first part of the first sentence (gaining a lot of 
> traction), and the first part of the second sentence (more difficult than 
> the traditional style), but the second part? Asynchronous processing is 
> *more efficient*?



It really depends on your definition of "efficient". Using async
generally introduces some overhead, so there's a cost. However it also
allows for the possibility of making better use of your compute
resources by doing useful work rather than idle-waiting for network
interactions to complete. 

As with many things - it's a useful tool and can be used to your
advantage, but you can also shoot yourself in the foot if used
inappropriately.
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[issue17972] inspect module docs omits many functions

[Paul Rudin]

Paul Rudin <p...@rudin.co.uk> added the comment:

Although formatannotation is undocumented, its actually documented as a default 
value for one of the parameters of formatargspec, so it does form part of the 
module's public interface. However formatargspec is deprecated, so it's still 
OK to deprecate formatannotation.

formatannotation is also used as a helper within Parameter, which isn't 
deprecated, but the public interface or docs of Parameter don't mention 
formatannotation, so using _formatannotation instead is fine.

Since I've looked through this and, as far as I can tell, nobody is working on 
it, I'll make the changes and make a PR.

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[issue17972] inspect module docs omits many functions

[Paul Rudin]

Paul Rudin <p...@rudin.co.uk> added the comment:

Documenting and generating a deprecation warning also makes them part of the 
documented public api. Or are you suggesting just the warning without including 
in the documentation?

Incidentally, there are also the classes BlockFinder and EndOfBlock, which are 
helpers for getblock and presumably not intended for public consumption.

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[issue17972] inspect module docs omits many functions

[Paul Rudin]

Paul Rudin <p...@rudin.co.uk> added the comment:

If some are to be considered private then the questions are: which ones and how 
to fix. Presumably renaming to start with "_" might break existing code, so 
maybe adding an __all__, and just including the public objects is better? That 
could break code existing relying on * imports I suppose. Deprecation is 
another possibility, although feels a little odd for things never documented.

formatannotation and formatannotationrelativeto look like a helper functions 
for formatargspec and are probably not intended as part of the public interface.

Similarly walktree looks like a helper for getclasstree (and its docstring 
describes it as such).

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Re: Python

[Paul Rudin]

Joaquin Alzola  writes:

> This email is confidential and may be subject to privilege. If you are not the
> intended recipient, please do not copy or disclose its content but contact the
> sender immediately upon receipt.

Probably best not to send it to a publicly accessible mailing list
then :/
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Re: Using namedtuples field names for column indices in a list of lists

[Paul Rudin]

"Deborah Swanson"  writes:

> Peter Otten wrote, on January 08, 2017 3:01 AM
>> 
>> columnA = [record.A for record in records]
>
> This is very neat. Something like a list comprehension for named tuples?

Not something like - this *is* a list comprehension - it creates a list
of named tuples.

The thing you iterate over within the comprehension can be any
iterator. (Of course you're going to run into problems if you try to
construct a list from an infinite iterator.)
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Re: Choosing a Python IDE. what is your Pythonish recommendation? I do

[Paul Rudin]

Tim Johnson  writes:

> * Antonio Caminero Garcia  [170102 20:56]:
>> Guys really thank you for your answers. Basically now I am more
>> emphasizing in learning in depth a tool and get stick to it so I
>> can get a fast workflow. Eventually I will learn Vim and its
>> python developing setup, I know people who have been programming
>> using Vim for almost 20 years and they did not need to change
>> editor (that is really awesome).
>
>  Bye the way, one thing I like about the GUI based vim is that it
>  supports tabs, where emacs does not.

M-x package-install tabbar

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Re: Clickable hyperlinks

[Paul Rudin]

"Deborah Swanson"  writes:

>
> I didn't try printing them before, but I just did. Got:
>
 print([Example](http://www.example.com)
>
> SyntaxError: invalid syntax  (arrow pointing at the colon)
>

With respect, if you typed that at python then it's probably a good idea to 
take a step back and work through the excellent tutorial.

https://docs.python.org/3/tutorial/

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Re: Choosing a Python IDE. what is your Pythonish recommendation? I do

[Paul Rudin]

Tim Johnson  writes:

> * Antonio Caminero Garcia  [170102 20:56]:
>> Guys really thank you for your answers. Basically now I am more
>> emphasizing in learning in depth a tool and get stick to it so I
>> can get a fast workflow. Eventually I will learn Vim and its
>> python developing setup, I know people who have been programming
>> using Vim for almost 20 years and they did not need to change
>> editor (that is really awesome).
>
>  Bye the way, one thing I like about the GUI based vim is that it
>  supports tabs, where emacs does not.

M-x package-install tabbar

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Re: Clickable hyperlinks

[Paul Rudin]

"Deborah Swanson"  writes:

>
> I didn't try printing them before, but I just did. Got:
>
 print([Example](http://www.example.com)
>   
> SyntaxError: invalid syntax  (arrow pointing at the colon)
>  

With respect, if you typed that at python then it's probably a good idea
to take a step back and work through the excellent tutorial.

https://docs.python.org/3/tutorial/

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Re: Choosing a Python IDE. what is your Pythonish recommendation? I do not know what to choose.

[Paul Rudin]

Tim Johnson  writes:

> * Antonio Caminero Garcia  [170102 20:56]:
>> Guys really thank you for your answers. Basically now I am more
>> emphasizing in learning in depth a tool and get stick to it so I
>> can get a fast workflow. Eventually I will learn Vim and its
>> python developing setup, I know people who have been programming
>> using Vim for almost 20 years and they did not need to change
>> editor (that is really awesome). 
>
>  Bye the way, one thing I like about the GUI based vim is that it
>  supports tabs, where emacs does not.

M-x package-install tabbar




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Re: Pyvenv puts both Python 2 and Python 3 in the same environment. Shocked!

[Paul Rudin]

Malik Rumi  writes:

> I just created a new venv using pyvenv from a 2.7 install. Now I am shocked to
> see that I can get both 2.7 and 3.4 in this same venv:
>
> (memory) malikarumi@Tetuoan2:~/Projects/cannon/New2.7Projects/memory$ python
> Python 2.7.12 (default, Nov 19 2016, 06:48:10) 
> [GCC 5.4.0 20160609] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
 exit()
> (memory) malikarumi@Tetuoan2:~/Projects/cannon/New2.7Projects/memory$ python3
> Python 3.4.2 (default, Apr 17 2015, 18:47:05) 
> [GCC 4.8.2] on linux
> Type "help", "copyright", "credits" or "license" for more information.

A venv doesn't remove everything from your path. Presumably python3 is
some system installed python. What does "which python3" say?

If you just invoke "python" then you'll get the venv one.


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Re: I am new to python. I have a few questions coming from an armature!

[Paul Rudin]

Lawrence D’Oliveiro <lawrenced...@gmail.com> writes:

> On Tuesday, August 16, 2016 at 6:26:01 PM UTC+12, Paul Rudin wrote:
>> sohcahtoa82 writes:
>>> squared_plus_one_list = map(lambda x: x**2 + 1, some_list)
>> 
>> I realise that this is about understanding lambda, but it's worth noting
>> in passing that we tend to write this sort of thing as:
>> 
>> squared_plus_one_list = [x**2 + 1 for x in some_list]
>
> The difference being that the “map” function takes an iterable and returns an 
> iterator.

Ah well - that depends the python version. Since the OP used a name
including the substring 'list' I assumed python 2.


> Why could this difference be important?

The main thing is to understand the difference, and then it's possible
to reason about whether it matters in a given context.

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Re: I am new to python. I have a few questions coming from an armature!

[Paul Rudin]

sohcahto...@gmail.com writes:

> On Monday, August 15, 2016 at 8:07:32 AM UTC-7, alister wrote:
>> On Mon, 15 Aug 2016 07:00:47 -0700, Sickfit92 wrote:
>> 
>> > 1. How long did it take you guys to master the language or, let me put
>> > it this way to completely get the hang and start writing code?
>> > 
> 
>> Some concepts took more time than others before I had the "Light bulb" 
>> moment, Comprehensions & decorators being the most notable although 
>> Lambda still escapes me, fortunately these can all be unrolled into 
>> larger functions so are not essential in the early stages
>> 
> 
>
> What helped me understand Lambdas is figuring out that they're really just a 
> $1,000 term for a $5 concept.
>
> A lambda is just a single-line function without a name (Unless you assign it 
> to one).  A syntactic shortcut.
>
> def square_plus_one(x):
> return x ** 2 + 1
>
> squared_plus_one_list = map(square_plus_one, some_list)
>
> is equivalent to:
>
> squared_plus_one_list = map(lambda x: x**2 + 1, some_list)

I realise that this is about understanding lambda, but it's worth noting
in passing that we tend to write this sort of thing as:

squared_plus_one_list = [x**2 + 1 for x in some_list]

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Re: Asynchronous programming

[Paul Rudin]

Steven D'Aprano  writes:

> Thanks to everyone who has answered, I think I'm slowly starting to get it
> now. Let's see if we can come up with a toy example that doesn't involve
> low-level socket programming :-)
>
> Let me simulate a slow function call:
>
>
> import random, time
>
> def work(id):
> print("starting with id", id)
> workload = random.randint(5, 15)
> for i in range(workload):
> time.sleep(0.2)  # pretend to do some real work
> print("processing id", id)  # let the user see some progress
> print("done with id", id)
> return 10 + id
>
>
> pending = [1, 2, 3, 4]
>
> for i, n in enumerate(pending):
> pending[i] = work(n)
>
>
> How do I write work() so that it cooperatively multi-tasks with other ...
> threads? processes? what the hell do we call these things? What does this
> example become in the asynchronous world?
>

They're not separate processes or threads, just think tasks that suspend
and restart cooperatively. You need some kind of event loop to
orchestrate running the tasks. Asyncio provides one.

You can do your example like this:

import asyncio, random

async def work(id):
print("starting with id", id)
workload = random.randint(5, 15)
for i in range(workload):
await asyncio.sleep(0.2)  # pretend to do some real work
print("processing id", id)  # let the user see some progress
print("done with id", id)
return 10 + id

loop = asyncio.get_event_loop()

pending = [1, 2, 3, 4]

jobs = [asyncio.ensure_future(work(n)) for n in pending]
 
loop.run_until_complete(asyncio.gather(*jobs))

loop.close()


> In this case, all the work is pure computation, so I don't expect to save
> any time by doing this, because the work is still all being done in the
> same process/thread, not in parallel. It may even take a little bit longer,
> due to the overhead of switching from one to another.
>

Yeah - you're not gaining anything here. All (?) the interesting use
cases involve waiting for something (e.g. disk access, network
communication, separate process) before you can proceed with your
computation.



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Re: Asynchronous programming

[Paul Rudin]

Steven D'Aprano  writes:

>
> But what's the point in doing it asynchronously if I have to just wait for
> it to complete?
>
>   begin downloading in an async thread
>   twiddle thumbs, doing nothing
>   process download

If you have nothing else to do, then there's no point.

But suppose you're implementing a web server. A request comes in - in
order to respond you need some data from a database. So you do the
database bit async. Whilst you're waiting for that you can get on with
processing other incoming requests.


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Re: Asynchronous programming

[Paul Rudin]

Chris Angelico  writes:

> On Thu, Aug 11, 2016 at 7:45 PM, Steven D'Aprano
>  wrote:
>> I don't know whether you would call that a callback. I suppose it could be, 
>> in
>> the sense that you might say:
>>
>> button.set_mouseup_function(mouseUp)
>>
>> but I'm used to thinking of it as a property of the button.
>
> "Callback" simply means "function that someone else calls". In fact,
> most dunder methods could be described as callbacks.
>


A callback is normally a callable you pass to some other function with
the expectation that it will be invoked in certain circumstances.


That's not really the same thing as something someone else calls: any
function that's part of a published api is intended to be called by
someone else; but that doesn't really make it a callback.


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Re: Asynchronous programming

[Paul Rudin]

Steven D'Aprano  writes:

>
> Is there a good beginner's tutorial introducing the basics of asynchronous
> programming? Starting with, why and where would you use it?

You could do worse than watch Dave Beazley's pycon talk:
https://www.youtube.com/watch?v=lYe8W04ERnY
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Re: log file.

[Paul Rudin]

Joaquin Alzola  writes:

> This email is confidential and may be subject to privilege. If you are
> not the intended recipient, please do not copy or disclose its content
> but contact the sender immediately upon receipt.

Probably not a good idea to send it to a publicly accessible resource
then :)

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Re: I'm wrong or Will we fix the ducks limp?

[Paul Rudin]

Paul Rudin <paul.nos...@rudin.co.uk> writes:

> Marko Rauhamaa <ma...@pacujo.net> writes:

>> So your "names" are *variables*.
>
> Informally yes, but "variable" has no meaning in the language reference.
>

... err sorry, actually not correct - but irrelevant to the point under
discussion.



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Re: I'm wrong or Will we fix the ducks limp?

[Paul Rudin]

Marko Rauhamaa <ma...@pacujo.net> writes:

> Paul Rudin <paul.nos...@rudin.co.uk>:
>
>> Marko Rauhamaa <ma...@pacujo.net> writes:
>>> The object is only an intermediate result; what is returned is a
>>> pointer (to an object), without an exception. That's not a matter of
>>> implementation. It's an essential part of Python's data model.
>>
>> Well - the language has no explicit notion of "pointer", [...] it's
>> better (IMO) to just talk in the terms the language specification
>> uses.
>
> The spec (https://docs.python.org/3/reference/datamodel.html>)
> uses the terms *identity* and *reference*, which are one-to-one.

identity isn't the same thing as a name, identity is an inherent
property of an object - many names may refer to the same object.

Similarly reference doesn't mean the same thing as identity. A reference
to an object can occur, for example:

["foo"]

The list refers to the string. There's no name involved anywhere. Both
the list and the string have an identity, but that's essentially
irrelevant to the fact that the list has a reference to the string.

>
>> There are names and objects, and mechanisms by which names come to
>> refer to objects according to the execution model.
>
> The spec as well as Python itself uses the word "name" for various
> strings:
>
>>>> "x".__class__.__name__
>'str'
>>>> __name__
>'__main__'
>

__name__ is not the same thing as what the spec means when it talks of a
name.

It's certainly true that a class declaration creates a binding from that
name to an object representing the class. But other names can equally
well refer to the same object:

>>> class Foo:
... pass
... 
>>> Bar = Foo
>>> x = Bar()
>>> x.__class__.__name__
'Foo'
>>>

>
> So your "names" are *variables*.

Informally yes, but "variable" has no meaning in the language reference.

>
> Your "mechanisms" are *references*.
>

Nope - when I spoke of mechanisms I was talking about the different
operational semantics by which a given names can be bound to an object.

Once such an binding has occured then I agree that the name refers to
the object in question.

> Your "objects" are *objects*.
>

I think I probably agree, but I'm not sure what you're saying - "object"
means something in the language reference - that's what I'm talking
about.


>> Talk of pointers is potentially confusing, because it carries baggage
>> from other languages which doesn't necessary map precisely onto the
>> python execution model.
>
> Unfortunately, virtually every word is overloaded and full of
> preconceived notions. Hence: "pegs", "leashes", "puppies".
>
> The main thing is to keep those three concepts apart from each other.
> Two notions will not suffice.
>

Well - adding more things is confusing in IMO - we have a language
reference, let's just use the terms in the language reference.

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Re: I'm wrong or Will we fix the ducks limp?

[Paul Rudin]

Marko Rauhamaa <ma...@pacujo.net> writes:

> Paul Rudin <paul.nos...@rudin.co.uk>:
>
>> Marko Rauhamaa <ma...@pacujo.net> writes:
>>> What is different is that in Python, every expression evaluates to a
>>> pointer. Thus, you can only assign pointers to variables.
>>
>> I don't think that's really right - every expression evaluates to an
>> object.
>
> The object is only an intermediate result; what is returned is a pointer
> (to an object), without an exception. That's not a matter of
> implementation. It's an essential part of Python's data model.
>

Well - the language has no explicit notion of "pointer", so I'm not sure
it's really correct to say that it's an essential part of the data
model. The way variables are used to reference the objects associated
with them from time to time has some similarities with pointer semantics
in other languages. But actually it's better (IMO) to just talk in the
terms the language specification uses. 

There are names and objects, and mechanisms by which names come to refer
to objects according to the execution model.


> (However, since "pointer" is evokes passions among crowds, it is better
> to use the neutral word "leash".)


Talk of pointers is potentially confusing, because it carries baggage
from other languages which doesn't necessary map precisely onto the
python execution model.


(The underlying cpython implementation, is neither here nor there - we
could in theory implement python in some other language which lacks a
pointer type.)

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Re: I'm wrong or Will we fix the ducks limp?

[Paul Rudin]

Marko Rauhamaa  writes:

> Antoon Pardon :
>
>> You can do something like that in simula, but only because
>> simula has two kinds of assignments. One kind that is
>> simular to python and one that is similar to C.
>> The one that is similar that python is the reference assignment.
>
> I see Python as doing the exact same thing with variables as C.

I'm not sure that's a good mental model of what's going on. A variable
declaration in C carries semantics of memory allocation to hold the
value. This isn't so in python

>
> What is different is that in Python, every expression evaluates to a
> pointer. Thus, you can only assign pointers to variables.
>

I don't think that's really right - every expression evaluates to an
object. Whether or not that object can be accessed through some variable
or not depends on how the expression is used.


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Re: Don't put your software in the public domain

[Paul Rudin]

Nobody  writes:

> On Sat, 04 Jun 2016 12:28:33 +1000, Steven D'Aprano wrote:
>
>>> OTOH, a Free software licence is unilateral; the author grants the user
>>> certain rights, with the user providing nothing in return.
>> 
>> That's not the case with the GPL.
>> 
>> The GPL requires the user (not the end-user, who merely avails themselves
>> of their common law right to run the software, but the developer user, who
>> copies, distributes and modifies the code) to do certain things in return
>> for the right to copy, distribute and modify the code:
>
> The GPL places limitations on the granted licence. That isn't the same
> thing as requiring the distributor to do something "in return".
>

The distributor grants the licence.

> This is why the (relatively few) cases where GPL infringements have
> resulted in litigation, the legal basis of the litigation is copyright
> infringement, not breach of contract.

Right, but the defence is that the licence grants permission to use; so
that's where the law if contract comes into it. You have to figure out
whether the use in question falls within the licence terms.

So if someone brings an action for copyright infringement you can argue
at least some of:

1. Copyright doesn't subsist in the copied material.
2. You didn't copy it.
3. One of the legal defences (fair use etc.) applies.
4. You had the permission of the copyright owner (i.e. a licence to copy
in these circumstances).


In the last case we're essentially into contract law.


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Re: Don't put your software in the public domain

[Paul Rudin]

Lawrence D’Oliveiro  writes:

> On Friday, June 3, 2016 at 9:53:47 PM UTC+12, Steven D'Aprano wrote:
>
>> A licence is something like a contract...
>
> A licence is quite different from a contract. A contract requires some
> indication of explicit agreement by both parties, a licence does not. That’s
> why Free Software licences only have to say something like “by using this
> software, you agree to the following terms...”, because if the user doesn’t
> accept the licence, then they have no licence.

But that's exactly what a contract is - an agreement. The licence is an
example, on the one side the copyright holder is agreeing not to sue the
user for copyright infringment and on the other the user is agreeing to
only use the code according to the terms.

>
> EULAs for proprietary software, on the other hand, try to have it both
> ways, by having a clause like the above, as well as requiring you to
> click an “I Agree” button or some such.

You can agree a contract by conduct...
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Re: Don't put your software in the public domain

[Paul Rudin]

Lawrence D’Oliveiro  writes:


> I wonder about the point of that, though; I have heard of cases where
> the judge ruled that the contract had been breached, and awarded
> damages of one pound/dollar/euro. So other than winning a symbolic
> victory, what was the point?

Damages for breach of contract are supposed to reflect the loss you
suffered as a result. A nominal award is basically saying, yes - the
other guy has failed to fulfil his contractual promise, but you haven't
actually suffered any real loss as a result.
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Re: Don't put your software in the public domain

[Paul Rudin]

Nobody  writes:

> On Fri, 03 Jun 2016 09:15:55 -0700, Lawrence D’Oliveiro wrote:
>
>>> [quoted text muted]
>> 
>> A licence is quite different from a contract. A contract requires some
>> indication of explicit agreement by both parties, a licence does not.
>
> More precisely, it requires "mutual consideration", i.e. each party must
> provide something of value to the other.

Don't confuse consideration with agreement - they're seperate legal
concepts.

Agreement is certainly necessary in pretty much all
jurisdictions. Consideration is required in most common law jurisdiction
(England, the US, most of the commonwealth) but not in many continental
legal systems.



> OTOH, a Free software licence is unilateral; the author grants the user
> certain rights, with the user providing nothing in return.

Nope - the user promises to abide by the terms of the licence. This is a
very common kind of consideration.
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Re: I'm wrong or Will we fix the ducks limp?

[Paul Rudin]

Sayth Renshaw  writes:

> Very briefly because I hope to shot down eloquently.
>
> Python is beautiful and is supposed to be a duck typed language, Yes?
>
> Then if I create and assign to a new variable with a list action why
> does the duck not quack?
>
> It feels wrong to spend a line writing what is already obvious
>

The problem is that you think that *variables* have a type. This isn't
the case. Objects have a type. A variable is a name by which you can
refer to an object. There are various ways in which you can associate a
object with a variable, the most obvious being an assignment statement.


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Re: Python on Windows with linux environment

[Paul Rudin]

Deborah Martin  writes:

> Try Cygwin at http://www.cygwin.com
>

Or use the new windows subsystem for linux:
https://blogs.windows.com/buildingapps/2016/03/30/run-bash-on-ubuntu-on-windows/
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Re: Quote of the day

[Paul Rudin]

Marko Rauhamaa <ma...@pacujo.net> writes:

> Paul Rudin <paul.nos...@rudin.co.uk>:
>
>> Marko Rauhamaa <ma...@pacujo.net> writes:
>>> The feeling of powerlessness can be crushing when you depend on a
>>> third-party component that is broken with no fix in sight.
>>
>> Presumably it depends on whether you have the source for the third
>> party component...
>
> Just having such an experience. The linux kernel has a critical bug in a
> major distribution (who shall be left unnamed here) that has been fixed
> in a later kernel version.
>
> Thanks to linux being free software, I managed to pin down the root
> cause after more than a month of debugging. I sent a bug report to the
> linux vendor and attached a tiny patch. The vendor has graciously agreed
> to consider releasing an update in the summer (we are in the process of
> verifying the fix).
>
> The problem was first detected in December. A semi-reliable reproduction
> was discovered in early February. The root cause and proposed fix was
> identified mid-March. A vendor fix will likely come out by the end of
> June.
>
> That's a long time to be without a product to sell.
>

But you do have the option of building a kernel incorporating your fix
and using that.

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Re: Quote of the day

[Paul Rudin]

Marko Rauhamaa  writes:

> Radek Holý :
>
>> 2016-05-17 9:50 GMT+02:00 Steven D'Aprano <
>> steve+comp.lang.pyt...@pearwood.info>:
>>
>>> Overhead in the office today:
>>>
>>> "I don't have time to learn an existing library - much faster to make
>>> my own mistakes!"
>>
>> *THUMBS UP* At least they are aware of that "own mistakes" part... Not
>> like my employer...
>
> Also:
>
>With a third party solution I don't need to fix the bugs.
>
>But with an in-house solution I at least *can* fix the bugs.
>
> The feeling of powerlessness can be crushing when you depend on a
> third-party component that is broken with no fix in sight.
>
>

Presumably it depends on whether you have the source for the third party
component...

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Re: Guido sees the light: PEP 8 updated

[Paul Rudin]

Pete Forman  writes:

> Why is it that Python continues to use a fixed width font and therefore
> specifies the maximum line width as a character count?

Python doesn't require the use of any particular font for editing your
code.

However programmers tend to use fixed width fonts when editing code
because then the visual representation of indentation works
consistently. But that's not a python specific thing.
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Re: [OT] fortran lib which provide python like data type

[Paul Rudin]

Marko Rauhamaa ma...@pacujo.net writes:

 Chris Angelico ros...@gmail.com:

 On Mon, Feb 2, 2015 at 12:59 PM, Steven D'Aprano
 steve+comp.lang.pyt...@pearwood.info wrote:
 And there are underspecified rules too. What is the plural of octopus? No
 fair looking it up in the dictionary.

 Standard and well-known piece of trivia, and there are several
 options. Octopodes is one of the most rigorously formal, but
 octopuses is perfectly acceptable. Octopi is technically
 incorrect, as the -us ending does not derive from the Latin.

 Your brain's grammar engine will give you the correct answer. It may not
 match your English teacher's answer, but the language we are talking
 about is not standard English but the dialect you have acquired in
 childhood.

Aha - the Humpty Dumpty approach to English usage: When I use a word it
means just what I choose it to mean...

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Re: Random ALL CAPS posts on this group

[Paul Rudin]

Rick Johnson rantingrickjohn...@gmail.com writes:


 No one here would justify a public business refusing to
 serve or employ a person based on race, religion, sex, or
 otherwise.

Depends on what you mean by or otherwise.

 So why would you so easily discriminate against speech?

People discriminate amongst prospective employees on the basis of what
the say all the time. It's the principle method by which you assess
candidates.


Freedom of expression is not about requiring others to publish your
words. It would be completely impractical - where would it end? Your own
slot on prime time TV to rant as you choose?


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Re: Python vs C++

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Sat, Aug 23, 2014 at 3:56 PM, dieter die...@handshake.de wrote:
 Chris Angelico ros...@gmail.com writes:
 Frankly, I wouldn't write OO in anything, because I think the entire
 concept of a WYSIWYG editor is flawed.

 That would limit (so called) office applications to experts only.
 But the success of these applications relies on the fact, that
 even a complete novice can immediately use them. For non-experts
 WYSIWYG editors are important.

 People say that. But WYSIWYG editors are the primary cause of
 frustrated yelling from the far end of the house, in my experience. I
 think they're an attractive nuisance. They're complicated to get right
 (pure WYSIWYG is useless, so you have to balance the visual benefit
 of being close to the result against the utility of seeing some of the
 non-printing information), and non-modular. With a text editor +
 compiler concept (whether the compiler's language is as big and
 complex as LaTeX or as simple as ReST), you can change editors without
 breaking anything. You don't like Libre Office Writer? Tough, there's
 no real alternative if you want to work on LO files.


The other problem is that because people are so used to using Word for
all text preparation we end up with Word files being used to carry
content for which plain text is just fine and would be preferable.

The conflation of text editing / word processing / desk top publishing
is problematic on a lot of levels.

I'm unconvinced is that e.g. LaTeX is inherently more expert that Word
for simple document preparation. It's mostly a question of familiarity.

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Re: Keep one GUI always on TOP while python code is running

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Fri, Aug 8, 2014 at 3:57 PM, Jaydeep Patil patil.jay2...@gmail.com wrote:
 I mean to say, One GUI should be always on top from start to end of code 
 running.
 So that user cant do any other operation.
 I am using wxpython

 Ah, that would be called System Modal, and should be reserved for
 absolutely critical system-wide alerts. It's also a feature that's
 simply not available to most user-space programs, and not available in
 most GUI toolkits.

 Short answer: Don't.

There are commercial software packages that do this sort of
thing. Examsoft is one - the idea being that people can take exams
without access to other software at the same time (so that, for example,
they could look at previously prepared notes).

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Re: OT: usenet reader software

[Paul Rudin]

Sturla Molden sturla.mol...@gmail.com writes:

 c...@isbd.net wrote:

 That doesn't address the problem at all! :-)  You still need a news
 reader.

 The problem was that Thunderbird does not support killfiles when used as a
 newsreader. Leafnode adds filtering capabilities which Thunderbird
 (supposedly) does not have.


There are plenty of non-Thunderbird news clients...
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Re: OT: usenet reader software

[Paul Rudin]

memilanuk memila...@gmail.com writes:

 Guess where I'm going with this is... is there anything out there worth trying
 - on Linux - that I'm missing?

emacs/gnus.
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Re: IDE for python

[Paul Rudin]

Terry Reedy tjre...@udel.edu writes:

 On 5/29/2014 5:41 AM, Wolfgang Maier wrote:
 On 28.05.2014 12:43, Sameer Rathoud wrote:
 Hello everyone,

 I am new to python.

 I am currently using python 3.3

 With python I got IDLE, but I am not very comfortable with this.

 What bothers you the most.

 Seems like not too many other people on this list share my opinion, but
 let me just say that IDLE is a nice and sufficient (for my purposes) IDE.
 If you're used to eclipse, then stick with it, but I prefer IDLE over
 any text editor although admittedly some of its keyboard shortcuts are
 unusual choices.

 I am curious how many of the editors people have been recommending have all of
 the following Idle features, that I use constantly.

 1. Run code in the editor with a single keypress.

 2. Display output and traceback in a window that lets you jump from the any
 line in the traceback to the corresponding file and line, opening the file if
 necessary.

 3. Search unopened files (grep) for a string or re.

 4. Display grep output in a window that lets you jump from any 'hit' to
 the corresponding file and line, opening the file if necessary.

Emacs.
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Re: Teaching python to non-programmers

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 On Thu, 10 Apr 2014 22:42:14 -0700, Rustom Mody wrote:

 In middle-eastern society women are expected to dress heavier than in
 the West. A few years ago a girl went to school in France with a scarf
 and she was penalized.

 Citation please. I think this is bogus...

This is not bogus. France has quite a strong tradition of keeping the
education system secular and has passed a law regarding the wearing of
ostentatious religious symbols in public schools, which also affects
things like the wearing of crosses.

Wikipedia has plenty on this...

http://en.wikipedia.org/wiki/Islamic_scarf_controversy_in_France

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Re: Teaching python to non-programmers

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Fri, Apr 11, 2014 at 2:37 PM, Rustom Mody rustompm...@gmail.com wrote:
 Right. Its true that when I was at a fairly large corporate, I was not told:
 Please always top post!

 What I was very gently and super politely told was:
 Please dont delete mail context

 Then you were told that by someone who does not understand email.

It's not necessarily a bad idea to retain context in corporate
emails. Messages tend to get forwarded to people other than the original
recipient(s), and the context can be very helpful.

But when you're posting to a mailing list or to a usenet group different
considerations apply as there's usually a way of seeing the whole
thread.

Email is often a poor relatively poor medium for internal communication,
because of this problem. Also people who might properly have a something
useful to say on the subject matter may never get to see the email.

A private news server or web forum is often better.

That's not to say that there's no place for email in internal
communication, but it's best reserved for occasions where
confidentiality is required, or at least politic.
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Re: Debugging on the Mac question.

[Paul Rudin]

Sean Murphy mhysnm1...@gmail.com writes:


 I am a Vision Impaired programmer on the Mac and Window platforms. I have
 started to learn Python. The biggest road block I have is the ability of
 debugging my simple scripts. The IDLE program does not work with the screen
 readers I use on the Mac or Windows. A screen reader is a program that grabs
 the text on the screen and converts it into speech output, at least this is 
 the
 5 feet explanation.  I cannot see the screen at all.

 I have looked at eclipse and it doesn't work with Voice-Over (the screen 
 reader
 on the Mac). I have java issues on my windows machine preventing me running
 this app.

 If I use $python -d script.py the debugger doesn't seem to trigger on the 
 mac. 

 So how I can perform a debug on a script so I can step through it, set up 
 break
 points, watch variables, etc.

 It is really annoying me, since under Perl I just added the -d switch and had 
 a
 full debugger that worked at the console level.

For command line debugging see
http://docs.python.org/3/library/pdb.html. 


More generally you might want to investigate
http://emacspeak.sourceforge.net/ (disclaimer - I have never used
this, but from what you say you might find it useful).
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Re: Got a Doubt ! Wanting for your Help ! Plz make it ASAP !

[Paul Rudin]

rusi rustompm...@gmail.com writes:

 Propositionally: All languages are equal -- Turing complete 

As an aside, not all languages are Turing complete. For example Charity
is a language with the property that programs are guaranteed to
terminate.

http://en.wikipedia.org/wiki/Charity_(programming_language)

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Re: Automation

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 A few minor errors is one thing, but when you see people whose posts are 
 full of error after error and an apparent inability to get English syntax 
 right, you have to wonder how on earth they expect to be a programmer? 

The irritating thing is apparent lack of care. A post is written once
and will be seen (perhaps not read) by many people. People post with the
intention of others reading their words. If they can't be bothered to
take a little care in writing, why should we spend time reading?
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Re: personal library

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Wed, Oct 30, 2013 at 1:00 PM, Dave Angel da...@davea.name wrote:
 First, I haven't seen any mention of a source control system.  Get one,
 learn it, and use it.  That should always hold your master copy.  And
 the actual repository should be on a system you can access from any of
 the others.

 Then, once you can get to such a repository, you use it to sync your
 various local copies on your individual machines.  You could have the
 synch happen automatically once a day, or whatever.  You could also
 build an auto-synch utility which pushed the synch from the server
 whenever the server was updated.

 If you're always going to be using these machines with real-time access
 to the central server, you could use Windows shares to avoid needing any
 updates.  Just create a share on the server, and mount it on each of the
 clients.  Add it to your system.path and you're done.

 I don't know about Mercurial, but with git it's pretty easy to set up
 a post-push hook that gets run whenever new changes hit the server.
From there, you could have some registered replicas that get
 immediately told to pull, which will give fairly immediate
 replication. It's not actually real-time, but you have a guarantee
 that they're up-to-date - if any change gets missed, it'll be caught
 in the next update. It'd take a little work to set up, but you could
 have something almost as convenient as shared folders but without the
 messes and risks.

 *Definitely* use source control.


Indeed. Also note that there's nothing per se wrong with putting your
repositories on Dropbox or similar - especially in a single user
situation. I do this so as to keep things synced across different
machines. You don't always want to check stuff in as you move from
e.g. laptop to desktop, but you do want to be able to pick up where you
left off on the other machine.


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Re: better and user friendly IDE recommended?

[Paul Rudin]

Joshua Landau jos...@landau.ws writes:

 If the time learning a set of tools is enough to make the choice
 between tools, I suggest avoiding, say, Vim.

That's a big if. 

If you expect to spend a lot of time editing text, code, etc. over the
next few years then it's definitely learning at least one of vim or
emacs to a reasonable degree of competency.
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Re: how to detect comment in source code file ?

[Paul Rudin]

Ben Finney ben+pyt...@benfinney.id.au writes:

 vnkumbh...@gmail.com writes:

 how works python interpreter for finding comment ?

 It works as specified in the language reference. In particular, see
 URL:http://docs.python.org/3/reference/lexical_analysis.html#comments.

 if possible find nested comment ?

 Python's comments are line-end comments only. The syntax does not allow
 multi-line nor nested comments.

Although you can use unbound multi-line strings as a kind of
comment. But its often better to make the strings into doc strings
proper.
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Re: user interfaces python3.x

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 On Mon, 02 Sep 2013 08:03:02 -0700, Paul Rice wrote:

 Im new to python3.x (well, programming as a whole. Never done before)
 and was wondering how do i get a proper interface instead of just
 writing. 

 A proper interface huh? Well, I'd love to tell you the answer...

...but holy wars would ensue.

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Re: semicolon at end of python's statements

[Paul Rudin]

Jussi Piitulainen jpiit...@ling.helsinki.fi writes:


 # Option 1.5
 for spam in sequence:
 if not predicate(spam): continue
 process(spam)

 This saves an indent level.

Just out of interest: is saving an indent level a useful thing?

I wouldn't lay out my code like that just because if you're coming back
to it later and reading through quickly it's (to my mind at least)
easier to miss what's going on.
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Re: How can I make this piece of code even faster?

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 On Sat, 20 Jul 2013 13:22:03 -0700, pablobarhamalzas asked:

 How can I make this piece of code even faster?

 - Use a faster computer.
 - Put in more memory.
 - If using Unix or Linux, decrease the nice priority of the process.

 I mention these because sometimes people forget that if you have a choice 
 between spend 10 hours at $70 per hour to optimize code, and spend 
 $200 to put more memory in, putting more memory in may be more cost 
 effective.


Sure - but it's helpful if programmers understand a little bit about the
computational complexity of algorithms. If it's just a question of
making each basic step of your algorithm a bit faster, then it may well
be better to spend money on better hardware than on squeezing more out
of your code. OTOH if you've got an n^2 implementation and there's
actually an n.log n solution available then you should probably re-code.

Of course if what you've got is actually adequate for your use-case then
it maybe that you don't actually need to do anything at all...
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Re: Editor Ergonomics [was: Important features for editors]

[Paul Rudin]

Roy Smith r...@panix.com writes:

  This is why I never understood the attraction of something like
 xemacs, where you use the mouse to make text selections and run
 commands out of menus.

Menus are good for learning the functionality, and you have them just as
much in Gnu emacs as in xemacs. You can even use them absent a windowing
system! Text selection with a mouse is a different thing. Sometimes it's
more convenient, sometimes it's not.

But I agree with your general point - it's often quicker to keep your
hands in position, which is where knowing keybinds for everything
scores.
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Re: sympy.nsimplify

[Paul Rudin]

Skip Montanaro s...@pobox.com writes:

 Very cool indeed.  In the comments was a link to an XKCD cartoon.  Its
 tool tip mentioned twin primes.  Looked that up.  Google pointed (of
 course) at Wikipedia.  Read that.  Backed up to the Google Search, and
 noticed there is a news item from 15 hours ago that an unknown
 mathematician at the University of New Hampshire has proven the twin
 primes conjecture:
 http://www.wired.com/wiredscience/2013/05/twin-primes/

 This is nothing to do with the original post.  It's just amazing to me
 how short the distance between one very interesting topic on the net
 and something almost unrelated can be.

AIUI the twin primes conjecture hasn't been proved. But a significant
related fact - that there's an infinitude of primes no more that N apart
where N ~ 70,000,000. That might not sound like a lot of progress - but
the point is that the existence of some finite bound is very
significant.
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Re: to a human - about 2to3

[Paul Rudin]

Jennifer Butler j.but...@albynschool.co.uk writes:

 Hiya

 I have trawled around your various pages and haven’t found what I
 want.

 I will start teaching Python to my pupils shortly. I have been looking
 for materials and have gathered a collection of programs. The problem
 is they are written in v2 and I have v3 installed in my classroom. I
 read about the 2to3 conversion program, but I can’t get it to work.

 Could you possibly give me a Noddy’s guide to do this?


Perhaps the first thing you should teach your students is how to ask
questions :)

When you say you can't get it to work what does that mean? What
exactly did you do? What happened as a result? How did that differ from
what you expected to happen or hoped would happen? Can you construct a
minimal specific example that illustrates your problem?




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Re: Iterating over files of a huge directory

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Tue, Dec 18, 2012 at 2:28 AM, Gilles Lenfant
 gilles.lenf...@gmail.com wrote:
 Hi,

 I have googled but did not find an efficient solution to my
 problem. My customer provides a directory with a hge list of
 files (flat, potentially 10+) and I cannot reasonably use
 os.listdir(this_path) unless creating a big memory footprint.

 So I'm looking for an iterator that yields the file names of a
 directory and does not make a giant list of what's in.

 Sounds like you want os.walk. 

But doesn't os.walk call listdir() and that creates a list of the
contents of a directory, which is exactly the initial problem?

 But... a hundred thousand files? I know the Zen of Python says that
 flat is better than nested, but surely there's some kind of directory
 structure that would make this marginally manageable?


Sometimes you have to deal with things other people have designed, so
the directory structure is not something you can control. I've run up
against exactly the same problem and made something in C that
implemented an iterator.

It would probably be better if listdir() made an iterator rather than a
list.
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Re: Help with unittest2

[Paul Rudin]

Thomas Bach thb...@students.uni-mainz.de writes:


 BTW, I actually never used 'assertTypeEqual' I rather call assertEqual
 and let unittest do the internals. I think assertEqual calls the right
 method for you depending on the arguments type. 


The assertTypeEqual methods have the advantage of checking the type of
the arguments. assertEqual would be OK with equal numerical arguments,
but that would be an inferior test if you were really expecting two
lists.

 If you want to make sure that something is of a certain type use
 assertIsInstance!

Yes, but why do something in 3 lines when there's a perfectly good
method provided that allows you do to it directly in one?

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Re: Python parser problem

[Paul Rudin]

Chris Angelico ros...@gmail.com writes:

 On Fri, Dec 14, 2012 at 6:12 AM, RCU alex.e.s...@gmail.com wrote:
   Dave,
 Thanks for the reply.
 The script was originally edited on Windows with proper \r\n endings,

 It's worth noting that many Windows-based editors and interpreters are
 quite happy with \n line endings. You may be able to save yourself
 some trouble by switching everything to Unix newlines.

... and in particular emacs for windows works well.

(holy wars ensue...)

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Re: python and Open cv

[Paul Rudin]

Zero Piraeus sche...@gmail.com writes:

 There aren't any rules about gmail (except the unwritten rule that to
 be a real geek you need to use a mail client that takes a whole
 weekend to configure, and another three years to properly understand).

Ha! 3 years? I've been using gnus for nearly 20 years and I still don't
understand it!
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Re: while expression feature proposal

[Paul Rudin]

Paul Rubin no.email@nospam.invalid writes:

 kind of ugly, makes me wish for a few more itertools primitives

JOOI, do you have specific primitives in mind?
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Re: Hiring Python Developer @ CA, USA

[Paul Rudin]

nithinm...@gmail.com writes:

 ...Must be an export in this language...

Are you hiring proof readers as well? :)
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Re: Search and replace text in XML file?

[Paul Rudin]

Terry Reedy tjre...@udel.edu writes:

 ... a proper text-editor*

  * ... Notepad++ is one such on Windows.

Surely emacs is the only such on any platform? :)

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Re: Finding duplicate file names and modifying them based on elements of the path

[Paul Rudin]

larry.mart...@gmail.com larry.mart...@gmail.com writes:

 It seems that if you do a list(group) you have consumed the list. This
 screwed me up for a while, and seems very counter-intuitive.

You've consumed the *group* which is an iterator, in order to construct
a list from its elements. Sorry if this is excessively nit-picking, but
it generally helps to keep these things very clear in your own mind.

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Re: Encapsulation, inheritance and polymorphism

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 For example, both ML and Haskell can, under some circumstances, report a 
 type-error for an infinite loop, *at compile time*.

... and in Charity all programs are guaranteed to terminate. Of course
it's not Turing complete.

http://en.wikipedia.org/wiki/Charity_(programming_language)
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Re: code review

[Paul Rudin]

Mark Lawrence breamore...@yahoo.co.uk writes:

 On 03/07/2012 03:25, John O'Hagan wrote:
 On Tue, 3 Jul 2012 11:22:55 +1000

 I agree to some extent, but as a counter-example, when I was a child there
 a subject called Weights and Measures which is now redundant because of the
 Metric system. I don't miss hogsheads and fathoms at all.

 John


 I weigh 13st 8lb - does this make me redundant?

It might mean that you have some redundant weight :)
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Re: Is that safe to use ramdom.random() for key to encrypt?

[Paul Rudin]

elvis-85...@notatla.org.uk writes:

 On 2012-06-17, Jon Clements jon...@googlemail.com wrote:

 Whatever you do - *do not* attempt to write your own algorithm. 

 very true


If everyone took that advice then we'd have a problem
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Re: Software Engineer -

[Paul Rudin]

Chris Withers ch...@simplistix.co.uk writes:

 On 11/03/2012 09:00, Blue Line Talent wrote:
 Blue Line Talent is looking for a mid-level software engineer with
 experience in a combination of

 Please don't spam this list with jobs, use the Python job board instead:

 http://www.python.org/community/jobs/

Just out of interest why do people object to job adverts here? Seems
harmless enough...
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Re: open office in another language?

[Paul Rudin]

Stefan Behnel stefan...@behnel.de writes:


 OOo has been fully scriptable in Python for ages. It even comes with an
 embedded Python runtime for that purpose (at least on
 non-package-management systems like Windows). So, Python is actually a
 standard component in all installations, whereas Java is not, and is
 therefore not necessarily available in a deployment. Basically, if you want
 your scripts to run in all OpenOffice/LibreOffice installations, you either
 have to write it in StarBasic, or use Python.

 The OOo extension API is called UNO, so look for the PyUNO bridge.
 Admittedly, it's somewhat badly documented, but it basically works the same
 way as the other UNO-API incarnations in other languages, so any UNO
 documentation will generally apply just fine.

 Also look for LibreOffice, as Ben Finney hinted. Since Oracle dropped Sun's
 OOo commitment, many regard it as the future of OOo. It's certainly the
 place where the development happens these days.

I have dabbled with PyUNO in the past. One issue is that the api seems
rather unpythonic (to me, at least).




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Re: Test None for an object that does not implement ==

[Paul Rudin]

GZ zyzhu2...@gmail.com writes:


 I run into a weird problem. I have a piece of code that looks like the
 following:

 f(, a=None, c=None):
 assert  (a==None)==(c==None)


There is only one 'None' - so use 'a is None' rather than 'a == None'.

(In common lisp there is a particular language construct that allows you
do determine whether an argument was passed in or was defaulted.)
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Re: % is not an operator

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:

 The existence of two potential answers for the remainder is certainly 
 correct, but the conclusion that remainder is not a binary operation 
 doesn't follow. It is a binary relation. 

This depends on your definition of operation. Normally an operation is
a function, rather than just a relation.
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Re: xml, minidom, ElementTree

[Paul Rudin]

Ethan Furman et...@stoneleaf.us writes:

 In the near future I will need to parse and rewrite parts of a xml files
 created by a third-party program (PrintShopMail, for the curious).
 It contains both binary and textual data.

 There has been some strong debate about the merits of minidom vs
 ElementTree.

 Recommendations?

I tend to start with BeautifulSoup, and think about other things if that
doesn't work out. It might just be me, but I find it easier to get stuff
done using BeautifulSoup than either minidom or ElementTree.
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Re: How to insert my own module in front of site eggs?

[Paul Rudin]

Roy Smith r...@panix.com writes:


 But, you're talking about installers.  I'm talking about if I've already 
 got something installed, how do I force one particular python process to 
 pull in a local copy of a module in preference to the installed one?

 In some cases, I own the machine and can make changes to /usr/local/lib 
 if I want to.  But what about on a shared machine?  I don't want to (or 
 perhaps can't) play with what's in /usr/local/lib just to make my stuff 
 load first.

Maybe I'm missing something - but if I want to do this I just mess about
with sys.path at the top of my python script/program. Always seems to
work... is there a situation in which it doesn't?

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Re: How to insert my own module in front of site eggs?

[Paul Rudin]

Roy Smith r...@panix.com writes:

 In article 874ny2fzn6@no-fixed-abode.cable.virginmedia.net,
  Paul Rudin paul.nos...@rudin.co.uk wrote:

 
 Maybe I'm missing something - but if I want to do this I just mess about
 with sys.path at the top of my python script/program. Always seems to
 work... is there a situation in which it doesn't?

 What if the first import of a module is happening inside some code you 
 don't have access to?

If you change sys.path first - before you do any imports - then any
other imports will surely come from the first thing on sys.path (unless
something else you import also changes sys.path)?



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Re: How to isolate a constant?

[Paul Rudin]

Gnarlodious gnarlodi...@gmail.com writes:

 Thanks for all those explanations, I've already fixed it with a tuple.
 Which is more reliable anyway.

neither of lists or tuples are more reliable than the other. They both
have perfectly well defined behaviour (which can be gleaned from reading
the documentation) and reliably behave as documented. You just have to
choose which fits better for the computation you're trying to implement.


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Re: revive a generator

[Paul Rudin]

Yingjie Lan lany...@yahoo.com writes:

 - Original Message -
 From: Paul Rudin paul.nos...@rudin.co.uk

 Generators are like that - you consume them until they run out of
 values. You could have done [x*x for x in range(3)] and then iterated
 over that list as many times as you wanted.
 
 A generator doesn't have to remember all the values it generates so it
 can be more memory efficient that a list. Also it can, for example,
 generate an infinite sequence.
 
 
 Thanks a lot to all who answered my question. 
 I am still not sure why should we enforce that 
 a generator can not be reused after an explicit 
 request to revive it?

The language has no explicit notion of a request to revive a
generator. You could use the same syntax to make a new generator that
yeilds the same values as the one you started with if that's what you
want. 

As we've already discussed if you want to iterate several times over the
same values then it probably makes sense to compute them and store them
in e.g. a list (although there are always trade-offs between storage use
and the cost of computing things again).



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Re: revive a generator

[Paul Rudin]

Yingjie Lan lany...@yahoo.com writes:



 What if the generator involves a variable from another scope,
 and before re-generating, the variable changed its value.
 Also, the generator could be passed in as an argument,
 so that we don't know its exact expression.

 vo = 34
 g = (vo*x for x in range(3))
 def myfun(g):
             for i in g: print(i)
             vo  += 3
             revive(g) #best if revived automatically
             for i in g: print(i)
 myfun(g)




I'm not really sure whether you intend g to yield the original values
after your revive or new values based on the new value of vo.  But
still you can make a class that supports the iterator protocol and does
whatever you want (but you can't use the generator expression syntax).

If you want something along these lines you should probably read up on
the .send() part of the generator protocol.

As an aside you shouldn't really write code that uses a global in that
way.. it'll end up biting you eventually.

Anyway... we can speculate endlessly about non-existent language
constructs, but I think we've probably done this one to death.
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Re: revive a generator

[Paul Rudin]

Yingjie Lan lany...@yahoo.com writes:

 Hi,

 it seems a generator expression can be used only once:

 g = (x*x for x in range(3))
 for x in g: print x
 0
 1
 4
 for x in g: print x #nothing printed


 Is there any way to revive g here?


Generators are like that - you consume them until they run out of
values. You could have done [x*x for x in range(3)] and then iterated
over that list as many times as you wanted.

A generator doesn't have to remember all the values it generates so it
can be more memory efficient that a list. Also it can, for example,
generate an infinite sequence.





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Re: 1/2 evaluates to 0

[Paul Rudin]

Laurent Claessens moky.m...@gmail.com writes:

 Hi all


 This is well known :

 1/2
 0

 This is because the division is an integer division.

 My question is : how can I evaluate 1/2 to 0.5 ? Is there some non
 integer division operator ?
 Up to now I workarounded writing float(1)/2. Is there an other way ?

from __future__ import division

Or use operator.truediv

Or use python 3.



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Re: Suggested coding style

[Paul Rudin]

Prasad, Ramit ramit.pra...@jpmorgan.com writes:

May I suggest a[n] email client that can group mailing list threads?

 Please do. Bonus points if it handles threading in a Gmail-like style.

The answer to any news/mail client with feature X type question is
normally gnus - although I don't know what Gmail-like style is.
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Re: Hierarchical commnd line parsing / help texts

[Paul Rudin]

Prasad, Ramit ramit.pra...@jpmorgan.com writes:

 This email is confidential...

Probably a bad idea to post it to a world readable mailing list then :)
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Re: Operator commutativity

[Paul Rudin]

Henrik Faber hfa...@invalid.net writes:


 How can I make this commutative?

Incidentally - this isn't really about commutativity at all - the
question is how can you define both left and right versions of add,
irrespective of whether they yield the same result.

I think __radd__ is what you're after.
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Re: Processing a large string

[Paul Rudin]

goldtech goldt...@worldpost.com writes:

 Hi,

 Say I have a very big string with a pattern like:

 akakksssk3dhdhdhdbddb3dkdkdkddk3dmdmdmd3dkdkdkdk3asnsn.

 I want to split the sting into separate parts on the 3 and process
 each part separately. I might run into memory limitations if I use
 split and get a big array(?)  I wondered if there's a way I could
 read (stream?) the string from start to finish and read what's
 delimited by the 3 into a variable, process the smaller string
 variable then append/build a new string with the processed data?

 Would I loop it and read it char by char till a 3...? Or?

 Thanks.

s = akakksssk3dhdhdhdbddb3dkdkdkddk3dmdmdmd3dkdkdkdk3asnsn
for k, subs in itertools.groupby(s, lambda x: x==3):
   print ''.join(subs)


what you actually do in the body of the loop depends on what you want to
do with the bits.
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Re: How can I make a program automatically run once per day?

[Paul Rudin]

John Salerno johnj...@gmail.com writes:

 I have a script that does some stuff that I want to run every day for
 maybe a week, or a month. So far I've been good about running it every
 night, but is there some way (using Python, of course) that I can make
 it automatically run at a set time each night?

Well - you can make a long lived python process that puts itself to
sleep for 24 hours and then wakes up and does stuff, but the normal
approach to this kind of thing is to use cron. On windows there's also
some kind of scheduler.

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Re: Does hashlib support a file mode?

[Paul Rudin]

Anssi Saari a...@sci.fi writes:

 Mel mwil...@the-wire.com writes:

 def file_to_hash(path, m = hashlib.md5()):

 hashlib.md5 *is* called once; that is when the def statement is executed.

 Very interesting, I certainly wasn't clear on this. So after that def,
 the created hashlib object is in the module's scope and can be
 accessed via file_to_hash.__defaults__[0].

This also why you have to be a bit careful if you use e.g. [] or {} as a
default argument - if you then modify these things within the function
you might not end up with what you expect - it's the same list or
dictionary each time the function is called.  So to avoid that kind of
thing you end up with code like:

def foo(bar=None):
   if bar is None:
   bar = []
   ...

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Re: TypeError: unbound method DefaultTracer() must be called with MyClass instance as first argument (got str instance instead)

[Paul Rudin]

Steven D'Aprano steve+comp.lang.pyt...@pearwood.info writes:


 Please don't post code with line numbers. That makes it difficult to copy
 and paste your function into an interactive session, so that we can run it
 and see what it does.

C-x r d

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Re: Fibonacci series recursion error

[Paul Rudin]

harrismh777 harrismh...@charter.net writes:

 lalit wrote:
 The above function return the
 return (fib(n-1)+fib(n-2))

 RuntimeError: maximum recursion depth exceeded in comparison
 [36355 refs]

 There is much debate about this generally, but general wisdom is that
 recursion is to be avoided when possible. Another way to say this is,
 Only use recursion when there is no other obvious way to handle the
 problem.
 Recursion is very tempting to young artists because its a ~cool trick,
 and because sometimes it requires very little coding (although huge
 amounts of memory!),  


Writing recurive code is acceptable and is a nice clear way of
expressing things when you have naturally recursive data structures, and
can lead to perfectly good compiled code. The problem in CPython is the
lack of tail optimization, so it's not a good idea for python . Some
language standards guarantee tail optimization...
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Re: Fibonacci series recursion error

[Paul Rudin]

Hans Georg Schaathun h...@schaathun.net writes:

 On Sat, 30 Apr 2011 06:43:42 +0100, Paul Rudin
   paul.nos...@rudin.co.uk wrote:
 :  Writing recurive code is acceptable and is a nice clear way of
 :  expressing things when you have naturally recursive data structures, and
 :  can lead to perfectly good compiled code. The problem in CPython is the
 :  lack of tail optimization, so it's not a good idea for python . Some
 :  language standards guarantee tail optimization...

 Well, if you run into a case where tail optimisation really makes a
 difference, you probably want to reimplement it for a compiler that
 guarantees tail optimisation, rather than reimplement it without
 recursion within python.

Clearly it makes a difference in any case where you'd hit the recursion
limit. It's no big deal to do your own unwinding of the recursion to a
loop, but the code is typically less clear.

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Re: Fibonacci series recursion error

[Paul Rudin]

Hans Georg Schaathun h...@schaathun.net writes:

 On Sat, 30 Apr 2011 12:29:00 +0100, Paul Rudin
   paul.nos...@rudin.co.uk wrote:
 :  Clearly it makes a difference in any case where you'd hit the recursion
 :  limit.

 What kind of problems make you hit the limit?

 Other than when you forget the base case, I mean.

Anytime you have enough data... there are plenty of things that are natural to
represent as recursive data structures, and often you don't know in
advance how much data your code is going to have to deal with.

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Re: Feature suggestion -- return if true

[Paul Rudin]

Teemu Likonen tliko...@iki.fi writes:

 I'm a simple Lisp guy who wonders if it is be possible to add some kind
 of macros to the language...

As a (now somewhat lapsed) long-time lisp programmer I sympathise with
the sentiment, but suspect that it's not going to gain serious traction
in python circles.
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Re: Directly Executable Files in Python

[Paul Rudin]

Benjamin Kaplan benjamin.kap...@case.edu writes:


 If you can figure out a good way to compile a language like Python,
 you'll be very rich. Yes, it is running the interpreter and then
 running the bytecode on the interpreter. It's the same way Java and
 .NET work.

Not exactly AIUI. .NET bytecodes do actually get compiled to executable code
before being executed (unless things have changed recently - I haven't
really done anything significant with .NET in the last couple of years).
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Re: best python games?

[Paul Rudin]

alex23 wuwe...@gmail.com writes:

 Paul Rudin paul.nos...@rudin.co.uk wrote:
 Apparently Eve Online is (stackless) python.

 I've dropped a ridiculous number of hours into EVE this year alone but
 I'd be very hesitant to ever mention best in relation to its
 coding :)

 It uses way too much floating point incorrectly, the in-game
 calculator gives the result of 878.53 - 874.20 as 4.32999. I'm
 pretty sure this is also why occasionally you'll be left with 1 0.01m3
 unit out of 39, with the storage container complaining it's full
 at 38,.99.


Floating point arithmetic isn't, in general, precise. I don't know the
game, so I can't comment on whether they should have chosen to ensure
precision in this context, but presumably that would make things a
little slower.
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Re: best python games?

[Paul Rudin]

sogeking99 neilalt300...@gmail.com writes:

 hey guys, what are some of the best games made in python? free games
 really. like pygames stuff. i want to see what python is capable of.

Apparently Eve Online is (stackless) python.
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Re: Easy function, please help.

[Paul Rudin]

Nanderson mandersonrandersonander...@gmail.com writes:


 loop would be infinite. I get what is happening in the function, and I
 understand why this would work, but for some reason it's confusing me
 as to how it is exiting the loop after a certain number of times. Help
 is appreciated, thanks.

It works because 0 tests false and because integer division yields
integers... eventually you'll get something like 1/10 giving 0.

It's not necessarily a good thing to rely on. For example if you try it
after from __future__ import division - or in python 3 - you'll get a
float as the result of the division and it won't test False.
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Re: Is Eval *always* Evil?

[Paul Rudin]

Robert Kern robert.k...@gmail.com writes:

 On 2010-11-10 17:14 , Christian Heimes wrote:
 Am 10.11.2010 18:56, schrieb Simon Mullis:

 Yes, eval is evil, may lead to security issues and it's unnecessary
 slow, too.

Still - it is used in the standard library...
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Re: Learning Pyhton - Functional Programming - How intersect/difference two dict with dict/values? fast!

[Paul Rudin]

Lawrence D'Oliveiro l...@geek-central.gen.new_zealand writes:

 In message mailman.787.1289336127.2218.python-l...@python.org, Terry Reedy 
 wrote:

 To echo John Nagle's point, if you want non-masochist volunteers to read
 your code, write something readable like:
 
 dict1 = {'ab': [[1,2,3,'d3','d4',5], 12],
   'ac': [[1,3,'78a','79b'], 54],
   'ad': [[56,57,58,59], 34],
   'ax': [[56,57,58,59], 34]}

 How come Python itself doesn’t display things that way?

try: pprint.pprint(dict1)
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Re: multiple discontinued ranges

[Paul Rudin]

xoff igor.idziejc...@gmail.com writes:

 I was wondering what the best method was in Python programming for 2
 discontinued ranges. e.g. I want to use the range 3 to 7 and 17 to 23.
 Am I obliged to use 2 for loops defining the 2 ranges like this:

 for i in range (3,7):
  do bla
 for i in range (7,17):
  do bla

 or is there a more clever way to do this?


for i in itertools.chain(xrange(3,7), xrange(17,23)):
print i
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Re: What is the best way to handle a missing newline in the following case

[Paul Rudin]

danmcle...@yahoo.com danmcle...@yahoo.com writes:

 The problem is when I get to the last line. When the program sees '\n'
 after the 9, everything works fine. However, when there isn't a '\n',
 the program doesn't process the last line.

 What would be the best approach to handle the case of the possible
 missing '\n' at the end of the file?

 use readines to read all lines into a list and then iterate thru the
 list:

 f = open(r'c:\test.txt', 'rb')
 print f.readlines()


 ['1\r\n', '3\r\n', '5\r\n', '7\r\n', '3\r\n', '9']

There's no real point in contructing a list. Just do

with open(r'c:\test.txt') as f:
   for l in f:
   print int(l) 

As long as you just have digits and whitespace then that's fine - int()
will do as you want.
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Re: What people are using to access this mailing list

[Paul Rudin]

John Bond li...@asd-group.com writes:

 On 3/11/2010 11:17 AM, Steven D'Aprano wrote:
 On Wed, 03 Nov 2010 08:02:29 +, John Bond wrote:

 Hope this isn't too O/T - I was just wondering how people read/send to
 this mailing list, eg. normal email client, gmane, some other software
 or online service?
 Usenet via my ISP, on comp.lang.python.



 Using what client (or web client)?


Emacs, of course :-;
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Re: Python documentation too difficult for beginners

[Paul Rudin]

Steven D'Aprano st...@remove-this-cybersource.com.au writes:

 A fair point -- the built-in open comes up as hit #30, whereas searching 
 for open in the PHP page brings up fopen as hit #1. But the PHP search 
 also brings up many, many hits -- ten pages worth.


OTOH googling for python open gives you the correct (for 2.7) page as
hit #1 - although you then have to use your browser's find facilty to
actually get to the description of the function in question.
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Re: functions, list, default parameters

[Paul Rudin]

Terry Reedy tjre...@udel.edu writes:

 Suppose I write an nasty C extension that mutates tuples. What then
 would be illegal about...

Depends on exactly what we mean by legal. If immutability is part of the
language spec (rather than an artifact of a particular implementation)
then a compiler could assume immutability.



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Re: embarrassing class question

[Paul Rudin]

Gregory Ewing greg.ew...@canterbury.ac.nz writes:

 Brendan wrote:
 I use
 Python sporadically, and frequently use the dir command to learn or
 remind myself of class methods.

 You can clean up dir() by defining __all__ as a list of
 names that you want to officially export. Other names will
 still be there, but they won't show up in the dir() listing.

I'm not sure that's necessarily a good idea... when you're trying to figure
out why something behaves in a certain way you want to check for the
presence of methods with special names.
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Re: is list comprehension necessary?

[Paul Rudin]

Andre Alexander Bell p...@andre-bell.de writes:

 I occasionally use LCs, if they seem useful. However, what I don't like
 about LCs is that they 'look-like' being a closed scope, while actually
 they are in the scope of there call. Example:

 i = 5
 l = [i**2 for i in range(3)]
 i
 2


Although:

p...@sleeper-service:~$ python3
Python 3.1.2 (r312:79147, Sep 27 2010, 09:57:50) 
[GCC 4.4.3] on linux2
Type help, copyright, credits or license for more information.
 i = 5
 l = [i**2 for i in range(3)]
 i
5
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