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Re: list comprehension misbehaving

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  Re: list comprehension misbehaving Tim Chase <python.list@tim.thechases.com> - 2013-03-28 10:44 -0500

#42150 — Re: list comprehension misbehaving

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

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