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Re: zip as iterator and bad/good practices

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From Terry Reedy <tjreedy@udel.edu>
Subject Re: zip as iterator and bad/good practices
Date Fri, 12 Jun 2015 19:43:08 -0400
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On 6/12/2015 4:34 PM, Laura Creighton wrote:
> The real problem is removing things from lists when you are iterating
> over them, not adding things to the end of lists.

One needs to iterate backwards.

 >>> ints = [0, 1, 2, 2, 1, 4, 6, 5, 5]

 >>> for i in range(len(ints)-1, -1, -1):
	if ints[i] % 2:
		del ints[i]
	
 >>> ints
[0, 2, 2, 4, 6]

But using a list comp and, if necessary, copying the result back into 
the original list is much easier.

 >>> ints = [0, 1, 2, 2, 1, 4, 6, 5, 5]
 >>> ints[:] = [i for i in ints if not i % 2]
 >>> ints
[0, 2, 2, 4, 6]


-- 
Terry Jan Reedy

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Thread

zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:00 +0200
  Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:05 +0200
  Re: zip as iterator and bad/good practices Ian Kelly <ian.g.kelly@gmail.com> - 2015-06-12 09:26 -0600
    Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:34 +0200
    Re: zip as iterator and bad/good practices Fabien <fabien.maussion@gmail.com> - 2015-06-12 17:59 +0200
  Re: zip as iterator and bad/good practices Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-06-12 17:22 +0100
  Re: zip as iterator and bad/good practices Laura Creighton <lac@openend.se> - 2015-06-12 22:34 +0200
  Re: zip as iterator and bad/good practices Terry Reedy <tjreedy@udel.edu> - 2015-06-12 19:27 -0400
  Re: zip as iterator and bad/good practices Terry Reedy <tjreedy@udel.edu> - 2015-06-12 19:43 -0400
    Re: zip as iterator and bad/good practices sohcahtoa82@gmail.com - 2015-06-12 17:02 -0700
      Re: zip as iterator and bad/good practices Chris Angelico <rosuav@gmail.com> - 2015-06-13 10:26 +1000
        Re: zip as iterator and bad/good practices sohcahtoa82@gmail.com - 2015-06-12 17:39 -0700
  Re: zip as iterator and bad/good practices jimages <jimages123@gmail.com> - 2015-06-13 13:32 +0800
    Re: zip as iterator and bad/good practices Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-13 07:17 +0000
      Re: zip as iterator and bad/good practices Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-06-13 13:48 +0100
        Re: zip as iterator and bad/good practices Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-06-13 16:16 +0000

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