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Date: Thu, 28 Mar 2013 10:44:51 -0500
From: Tim Chase <python.list@tim.thechases.com>
To: Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de>
Subject: Re: list comprehension misbehaving
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References: <loom.20130328T160914-263@post.gmane.org>
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Xref: csiph.com comp.lang.python:42150

On 2013-03-28 15:25, Wolfgang Maier wrote:
> Dear all, with
> a=list(range(1,11))
> 
> why (in Python 2.7 and 3.3) is this explicit for loop working:
> for i in a[:-1]:
>     a.pop() and a

As you discover:

> Especially, since these two things *do* work as expected:
> [a.pop() and a[:] for i in a[:-1]]

it's because you're taking a snapshot copy of "a" in the middle of
the loop.  In your first example, if you change it to

  results = []
  for i in a[:-1]:
    results.append(a.pop() and a)
  print results

you get the same thing as your list comprehension because each item
in "results" refers to the now-(mostly)empty "a".

-tkc