[Python-Dev] Re: comprehension abbreviation (was: Adding any() andall())

Alex Martelli aleaxit at yahoo.com
Wed Mar 30 08:45:10 CEST 2005

On Mar 29, 2005, at 17:41, Terry Reedy wrote:
> "Steve Holden" <steve at holdenweb.com> wrote in message
> news:d2asg9$3tf$1 at sea.gmane.org...
>> Having to write
>>     [x for x in seq]
>> to produce a copy of a list doesn't seem that outrageous to me,
> Except for (currently) leaving the last value of sequence bound to 'x'
> after making the copy, how is the above different from list(seq)?

Well, it's less concise, and over an order of magnitude slower:

Nimue:~/pypy alex$ python2.4 -mtimeit -s'seq=range(1000)' '[x for x in 
1000 loops, best of 3: 312 usec per loop
Nimue:~/pypy alex$ python2.4 -mtimeit -s'seq=range(1000)' 'list(seq)'
10000 loops, best of 3: 24.3 usec per loop

I fail to see any advantages to compensate for these minuses.


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