Re: Strange behavior

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Date	Wed, 15 Aug 2012 07:55:58 +1000
Subject	Re: Strange behavior
From	Chris Angelico <rosuav@gmail.com>
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On Wed, Aug 15, 2012 at 1:38 AM,  <light1quark@gmail.com> wrote:
> def testFunc(startingList):
>         xOnlyList = [];
>         for str in startingList:
>                 if (str[0] == 'x'):
>                         print str;
>                         xOnlyList.append(str)
>                         startingList.remove(str) #this seems to be the problem
>         print xOnlyList;
>         print startingList
> testFunc(['xasd', 'xjkl', 'sefwr', 'dfsews'])

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.)

(Unrelated side point: Putting parentheses around the print statements
makes them compatible with Python 3, in which 'print' is a function.
Unless something's binding you to Python 2, consider working with the
current version - Python 2 won't get any more features added to it any
more.)

Python's an awesome language. You may have to get your head around a
few new concepts as you shift thinking from PHP's, but it's well worth
while.

Chris Angelico

Thread

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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