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Re: Extracting elements over multiple lists?

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From Terry Reedy <tjreedy@udel.edu>
Subject Re: Extracting elements over multiple lists?
Date Mon, 07 Nov 2011 19:06:53 -0500
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On 11/7/2011 1:22 PM, John Gordon wrote:
> In<cf007146-3a08-44c4-bf01-d1a9253c83e3@o19g2000vbk.googlegroups.com>  JoeM<josephmeiring@gmail.com>  writes:
>
>> Thanks guys, I was just looking for a one line solution instead of a
>> for loop if possible. Why do you consider
>
>> [x.remove(x[0]) for x in [a,b,c]]
>
>> cheating? It seems compact and elegant enough for me.

It looks like incomplete code with 'somelists = ' or other context 
omitted. It saves no keypresses '[',...,SPACE,...,']' versus 
...,':',ENTER,TAB,... . (TAB with a decent Python aware editor.)

> I wouldn't call it cheating, but that solution does a fair bit of
> unneccessary work (creating a list comprehension that is never used.)

The comprehension ( the code) is used, but the result is not. If the 
source iterator has a large number of items rather than 3, the throwaway 
list could become an issue. Example.

fin = open('source.txt')
fout= open('dest.txt, 'w')
for line in fin:
   fout.write(line.strip())
# versus
[fout.write(line.strip()) for line in fin]

If source.txt has 100 millions lines, the 'clever' code looks less 
clever ;=). Comprehensions are intended for creating collections (that 
one actually wants) and for normal Python coding are best used for that.

-- 
Terry Jan Reedy

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Thread

Extracting elements over multiple lists? JoeM <josephmeiring@gmail.com> - 2011-11-07 09:12 -0800
  Re: Extracting elements over multiple lists? John Gordon <gordon@panix.com> - 2011-11-07 17:37 +0000
  Re: Extracting elements over multiple lists? Laurent Claessens <moky.math@gmail.com> - 2011-11-07 18:44 +0100
    Re: Extracting elements over multiple lists? JoeM <josephmeiring@gmail.com> - 2011-11-07 10:01 -0800
      Re: Extracting elements over multiple lists? John Gordon <gordon@panix.com> - 2011-11-07 18:22 +0000
        Re: Extracting elements over multiple lists? Terry Reedy <tjreedy@udel.edu> - 2011-11-07 19:06 -0500
      Re: Extracting elements over multiple lists? Peter Otten <__peter__@web.de> - 2011-11-07 19:33 +0100
      Re: Extracting elements over multiple lists? Jean-Michel Pichavant <jeanmichel@sequans.com> - 2011-11-07 19:51 +0100
      Re: Extracting elements over multiple lists? Dave Angel <d@davea.name> - 2011-11-07 15:06 -0500
      Re: Extracting elements over multiple lists? Laurent Claessens <moky.math@gmail.com> - 2011-11-08 08:07 +0100
      RE: Extracting elements over multiple lists? "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2011-11-15 17:01 +0000
        Re: Extracting elements over multiple lists? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-15 22:21 +0000
      Re: Extracting elements over multiple lists? Dave Angel <d@davea.name> - 2011-11-15 13:17 -0500
      Re: Extracting elements over multiple lists? Chris Angelico <rosuav@gmail.com> - 2011-11-16 06:53 +1100
        Re: Extracting elements over multiple lists? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-11-15 22:25 +0000
          Re: Extracting elements over multiple lists? Chris Angelico <rosuav@gmail.com> - 2011-11-16 09:54 +1100
    Re: Extracting elements over multiple lists? Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2011-11-07 19:06 +0100

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