Re: Evaluate once or every time
On 2/24/2023 7:00 PM, 2qdxy4rzwzuui...@potatochowder.com wrote: On 2023-02-24 at 18:42:39 -0500, Thomas Passin wrote: VOWELS = 'aeiouAEIOU' is_vowel = 'y' in VOWELS If I really needed them to be in a list, I'd probably do a list comprehension: VOWEL_LIST = [ch for ch in VOWELS] Why use a comprehension when a simple loop will do? ;-) No. Wait. That's not what I meant. Why use a comprehension when the constructor will do? VOWEL_LIST = list(VOWELS) It just didn't occur to me, I think, that this would create a list of the string's characters. Very nice! -- https://mail.python.org/mailman/listinfo/python-list
Re: Evaluate once or every time
On 2023-02-24 at 18:42:39 -0500, Thomas Passin wrote: > VOWELS = 'aeiouAEIOU' > is_vowel = 'y' in VOWELS > > If I really needed them to be in a list, I'd probably do a list > comprehension: > > VOWEL_LIST = [ch for ch in VOWELS] Why use a comprehension when a simple loop will do? ;-) No. Wait. That's not what I meant. Why use a comprehension when the constructor will do? VOWEL_LIST = list(VOWELS) -- https://mail.python.org/mailman/listinfo/python-list
Re: Evaluate once or every time
On 2/24/2023 5:35 PM, avi.e.gr...@gmail.com wrote:
Mark,
I was very interested in the point you made and have never thought much about
string concatenation this way but adjacency is an operator worth using.
This message has a new subject line as it is not about line continuation or
comments.
From what you say, concatenation between visibly adjacent strings is done once
when generating bytecode. Using a plus is supposed to be about the same but may
indeed result in either an error if you use anything other than a string literal
bad = "hello " str(12)
or you must use something like a "+" to do the concatenation at each run time.
Or, weirder, do it manually as :
good = "hello ".__add__(str(12))
This may be no big deal in terms of efficiency but something to consider.
I have often stared in amazement at code like:
mylist = "The quick brown fox jumps over the lazy dog".split()
mylist
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']
Why be amazed? The .split() version is way easier to type. I do it all
the time. Usually these evaluations will be done only once, at compile
time, so the cost in computing time is usually not important. And, if
you get right down to it, the first form is actually what you mean. The
second form is an implementation detail (you need to feed a list of
words into a function).
Or perhaps to make a list of vowels:
import string
vowels = list("aeiouAEIOU")
consonants = sorted(list(set(string.ascii_letters) - set(vowels)))
I mean couldn't you do this work in advance and do something like:
vowels = ['A', 'E', 'I', 'O', 'U', 'a', 'e', 'i', 'o', 'u']
consonants = ['B', 'C', 'D', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q',
'R', 'S', 'T', 'V', 'W', 'X', 'Y', 'Z', 'b', 'c', 'd', 'f', 'g', 'h', 'j', 'k',
'l', 'm', 'n', 'p', 'q', 'r', 's', 't', 'v', 'w', 'x', 'y', 'z']
I don't want to have to type these monsters, and in this form I'd be
prone to making an error. And they are hard to proofread. Anyway, a
list like this is typically used to assess whether a character is in one
or the other group, and you can do it without turning the string into a
list of characters:
VOWELS = 'aeiouAEIOU'
is_vowel = 'y' in VOWELS
If I really needed them to be in a list, I'd probably do a list
comprehension:
VOWEL_LIST = [ch for ch in VOWELS]
Again, much easier to type and to read, closer to what is really meant,
and less error-prone.
In the case of the consonants, even in string form it would be hard to
proofread, so I'd be inclined to insert spaces for readability:
CONSONANTS = 'BCDFGH JKLMNP QRSTVWX YZ bcdfgh jklmnp qrstvwx yz'
If for some reason spaces wouldn't work, I'd delete them:
CONSONANTS = CONSONANTS.replace(' ', '')
In concept this isn't much different from using the C pre-processor to
pre-compute some things for you.
I assume this latter version would be set once no matter how often you run the
unchanged program. YES, I am aware this may be bad practice for code you want
to adapt for international use.
But why be wasteful? I am currently reading a book on refactoring and will not
share if it is illustrated, or if the above is a decent example as the book
uses examples in JavaScript.
--
https://mail.python.org/mailman/listinfo/python-list
Re: Evaluate once or every time
On Sat, 25 Feb 2023 at 09:36, wrote: > From what you say, concatenation between visibly adjacent strings is done > once when generating bytecode. Using a plus is supposed to be about the same > but may indeed result in either an error if you use anything other than a > string literal > > bad = "hello " str(12) > > or you must use something like a "+" to do the concatenation at each run > time. Or, weirder, do it manually as : > Abuttal is a syntactic feature. It's completely different from string concatenation. The only similarity is that some forms of addition may be constant-folded. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
Evaluate once or every time
Mark,
I was very interested in the point you made and have never thought much about
string concatenation this way but adjacency is an operator worth using.
This message has a new subject line as it is not about line continuation or
comments.
From what you say, concatenation between visibly adjacent strings is done once
when generating bytecode. Using a plus is supposed to be about the same but may
indeed result in either an error if you use anything other than a string literal
bad = "hello " str(12)
or you must use something like a "+" to do the concatenation at each run time.
Or, weirder, do it manually as :
good = "hello ".__add__(str(12))
This may be no big deal in terms of efficiency but something to consider.
I have often stared in amazement at code like:
>>> mylist = "The quick brown fox jumps over the lazy dog".split()
>>> mylist
['The', 'quick', 'brown', 'fox', 'jumps', 'over', 'the', 'lazy', 'dog']
Or perhaps to make a list of vowels:
import string
vowels = list("aeiouAEIOU")
consonants = sorted(list(set(string.ascii_letters) - set(vowels)))
I mean couldn't you do this work in advance and do something like:
vowels = ['A', 'E', 'I', 'O', 'U', 'a', 'e', 'i', 'o', 'u']
consonants = ['B', 'C', 'D', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q',
'R', 'S', 'T', 'V', 'W', 'X', 'Y', 'Z', 'b', 'c', 'd', 'f', 'g', 'h', 'j', 'k',
'l', 'm', 'n', 'p', 'q', 'r', 's', 't', 'v', 'w', 'x', 'y', 'z']
I assume this latter version would be set once no matter how often you run the
unchanged program. YES, I am aware this may be bad practice for code you want
to adapt for international use.
But why be wasteful? I am currently reading a book on refactoring and will not
share if it is illustrated, or if the above is a decent example as the book
uses examples in JavaScript.
-Original Message-
From: Python-list On
Behalf Of Mark Bourne
Sent: Friday, February 24, 2023 4:04 PM
To: python-list@python.org
Subject: Re: Line continuation and comments
Personally, I don't particularly like the way you have to put multiline strings
on the far left (rather than aligned with the rest of the scope) to avoid
getting spaces at the beginning of each line. I find it makes it more
difficult to see where the scope of the class/method/etc.
actually ends, especially if there are multiple such strings. It's not too bad
for strings defined at the module level (outer scope) though, and of course for
docstrings the extra spaces at the beginning of each line don't matter.
However, rather than using "+" to join strings as in your examples (which, as
you suggest, is probably less efficient), I tend to use string literal
concatenation which I gather is more efficient (treated as a single string at
compile-time rather than joining separate strings at run-time). See
.
For example:
HelpText = ("Left click: Open spam\n"
"Shift + Left click: Cook spam\n"
"Right click:Crack egg\n"
"Shift + Right click:Fry egg\n")
The downside is having to put an explicit "\n" at the end of each line, but to
me that's not as bad as having to align the content to the far left.
Getting a bit more on topic, use of backslashes in strings is a bit different
to backslashes for line continuation anyway. You could almost think of "\
(newline)" in a multiline string as being like an escape sequence meaning
"don't actually put a newline character in the string here", in a similar way
to "\n" meaning "put a newline character here" and "\t"
meaning "put a tab character here".
Mark.
avi.e.gr...@gmail.com wrote:
> Good example, Rob, of how some people make what I consider RELIGIOUS edicts
> that one can easily violate if one wishes and it makes lots of sense in your
> example.
>
> Let me extend that. The goal was to store a character string consisting of
> multiple lines when printed that are all left-aligned. Had you written:
>
> HelpText = """
> Left click: Open spam
> ...
> Shift + Right click:Fry egg
> """
> Then it would begin with an extra carriage return you did not want. Your
> example also ends with a carriage return because you closed the quotes on
> another line, so a \ on the last line of text (or moving the quotes to the
> end of the line) would be a way of avoiding that.
>
> Consider some alternatives I have seen that are in a sense ugly and may
> involve extra work for the interpreter unless it is byte compiled once.
>
> def someFunc():
> HelpText =
> "Left click: Open spam" + "\n" +
> "Shift + Left click: Cook spam" + "\n" +
> ...
>
> Or the variant of:
> HelpText = "Left click: Open spam\n"
> HelpText += " Shift + Left click: Cook spam\n"
> ...
>
> Or perhaps just dumping the multi-line text into a file beforehand and
>
