Guido's regrets: filter and map

[Dennis Lee Bieber]

maney at pobox.com fed this fish to the penguins on Sunday 24 November 
2002 07:40 am:

> 
> ### revised test with filtering
> from time import time
> 
> n = 1000000
> N = xrange(n)
> 
> t0 = time()
> S=[]
> a = S.append
> for x in N:
>     if x % 2 == 1:
>         a(str(x))
> print 'for loop took %.2f to make a list of %d items' % ((time()-t0),
> len(S))
> 
> del S
> t0 = time()
> S = [str(x) for x in N if x % 2 == 1]
> print 'list comprehension took %.2f to make a list of %d items' %
> ((time()-t0), len(S))
> 
> del S
> t0 = time()
> S = map(str,filter(lambda x: x % 2 == 1, N))
> print 'map took %.2f to make a list of %d items' % ((time()-t0),
> len(S))
> ###
> 
        <snip>

> Okay, that's enough for now.

        Well, to add some more embers... Two runs under Mandrake 8.2, on a 
733MHz P-III with RDRAM (Dell XPS B733r), Python 2.2, using the program 
listed above.

[wulfraed at beastie wulfraed]$ python t.py
for loop took 7.61 to make a list of 500000 items
list comprehension took 7.30 to make a list of 500000 items
map took 6.84 to make a list of 500000 items
[wulfraed at beastie wulfraed]$ python t.py
for loop took 7.61 to make a list of 500000 items
list comprehension took 7.31 to make a list of 500000 items
map took 6.85 to make a list of 500000 items

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