Language Shootout

[Andrew Gaul]

In article <mailman.994689198.3317.python-list at python.org>, Roman Suzi wrote:
> One more point about shootout. If I understood correctly, advanced
> features are banned. You can't change
> 
> k = []
> for i in list:
>   k.append(f(i)
> 
> into:
> 
> k = [f(i) for i in list]

Actually, the former isn't much slower than the latter.  Using map is
almost twice as fast.  I believe that map generates the result list by
calling len() on the source list, avoiding the cost of growing the
result list.  I suppose list comprehensions could be implemented such
that if there were not a filter clause, to prealloacte the list.  But
then, one should be using map anyway (you're only saving an implicit
lambda using a list comprehension).


meatring [~]$ time python2.1 -c 'k = []
for x in xrange(1000000):
    k.append(x)'

real    0m3.934s
user    0m3.440s
sys     0m0.490s

meatring [~]$ time python2.1 -c '[ x+1 for x in xrange(1000000) ]'

real    0m3.402s
user    0m2.670s
sys     0m0.720s

meatring [~]$ time python2.1 -c 'map(lambda x: x+1, xrange(1000000))'

real    0m1.899s
user    0m1.840s
sys     0m0.060s

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