GOTCHA with list comprehension

Newsgroups	comp.lang.python
Date	2015-08-04 23:48 -0700
Message-ID	<ebf0a31e-1021-41d2-affb-8318838a464b@googlegroups.com> (permalink)
Subject	GOTCHA with list comprehension
From	Pavel S <pavel@schon.cz>

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Hi,

I recently found interesting GOTCHA while doing list comprehension in python 2.6:

>>> values = ( True, False, 1, 2, 3, None )
>>> [ value for value in values if value if not None ]
[True, 1, 2, 3]

I was wondering why this list comprehension returns incorrect results and finally found a typo in the condition. The typo wasn't visible at the first look.

My intention was: if value is not None
But I wrote: if value if not None

Is that a language feature of list comprehension that it accepts conditions like: if A if B if C if D ...?

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GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-04 23:48 -0700
  Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:03 -0700
    Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:20 +1000
  Re: GOTCHA with list comprehension Peter Otten <__peter__@web.de> - 2015-08-05 09:04 +0200
  Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:05 +1000
    Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:10 -0700
      Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 17:21 +1000
        Re: GOTCHA with list comprehension Pavel S <pavel@schon.cz> - 2015-08-05 00:33 -0700
    Re: GOTCHA with list comprehension Marko Rauhamaa <marko@pacujo.net> - 2015-08-05 12:01 +0300
      Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-05 19:52 +1000
        Re: GOTCHA with list comprehension Marko Rauhamaa <marko@pacujo.net> - 2015-08-05 14:10 +0300
      Re: GOTCHA with list comprehension Saran Ahluwalia <ahlusar.ahluwalia@gmail.com> - 2015-08-07 09:08 -0400
  Re: GOTCHA with list comprehension Laura Creighton <lac@openend.se> - 2015-08-06 06:39 +0200
  Re: GOTCHA with list comprehension Chris Angelico <rosuav@gmail.com> - 2015-08-06 14:44 +1000

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