Re: Strange behavior

From	Alain Ketterlin <alain@dpt-info.u-strasbg.fr>
Newsgroups	comp.lang.python
Subject	Re: Strange behavior
Date	2012-08-15 11:50 +0200
Organization	Universites Paris VI/Paris VII - France
Message-ID	<87has4pjpx.fsf@dpt-info.u-strasbg.fr> (permalink)
References	<1a1834ae-2b4a-473f-b626-f37a17588199@googlegroups.com> <mailman.3289.1344981361.4697.python-list@python.org>

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Chris Angelico <rosuav@gmail.com> writes:

> Other people have explained the problem with your code. I'll take this
> example as a way of introducing you to one of Python's handy features
> - it's an idea borrowed from functional languages, and is extremely
> handy. It's called the "list comprehension", and can be looked up in
> the docs under that name,
>
> def testFunc(startingList):
>     xOnlyList = [strng for strng in startingList if strng[0] == 'x']
>     startingList = [strng for strng in startingList if strng[0] != 'x']
>     print(xOnlyList)
>     print(startingList)
>
> It's a compact notation for building a list from another list. (Note
> that I changed "str" to "strng" to avoid shadowing the built-in name
> "str", as others suggested.)

Fully agree with you: list comprehension is, imo, the most useful
program construct ever. Extremely useful.

But not when it makes the program traverse twice the same list, where
one traversal is enough.

-- Alain.

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Strange behavior light1quark@gmail.com - 2012-08-14 08:38 -0700
  Re: Strange behavior Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-08-14 17:59 +0200
    Re: Strange behavior Terry Reedy <tjreedy@udel.edu> - 2012-08-14 15:05 -0400
  Re: Strange behavior Virgil Stokes <vs@it.uu.se> - 2012-08-14 21:40 +0200
    Re: Strange behavior Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-15 00:19 +0000
      Re: Strange behavior Virgil Stokes <vs@it.uu.se> - 2012-08-16 13:18 +0200
        Re: Strange behavior Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 17:40 +0000
      Re: Strange behavior Peter Otten <__peter__@web.de> - 2012-08-16 15:02 +0200
  Re: Strange behavior light1quark@gmail.com - 2012-08-14 12:20 -0700
    Re: Strange behavior Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-08-15 11:57 +0200
  Re: Strange behavior Chris Angelico <rosuav@gmail.com> - 2012-08-15 07:55 +1000
    Re: Strange behavior Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-08-15 11:50 +0200

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