Is there a map without result in python?

Question

Sometimes, I just want to execute a function for a list of entries -- eg.:

for x in wowList:
   installWow(x, 'installed by me')

Sometimes I need this stuff for module initialization, so I don't want to have a footprint like x in global namespace. One solution would be to just use map together with lambda:

map(lambda x: installWow(x, 'installed by me'), wowList)

But this of course creates a nice list [None, None, ...] so my question is, if there is a similar function without a return-list -- since I just don't need it.

(off course I can also use _x and thus not leaving visible footprint -- but the map-solution looks so neat ...)

Answer 1

I can not resist myself to post it as separate answer

reduce(lambda x,y: x(y, 'installed by me') , wowList, installWow)

only twist is installWow should return itself e.g.

def installWow(*args):
    print args
    return installWow

Answer 2

I tested several different variants, and here are the results I got.

Python 2:

>>> timeit.timeit('for x in xrange(100): L.append(x)', 'L = []')
14.9432640076
>>> timeit.timeit('[x for x in xrange(100) if L.append(x) and False]', 'L = []')
16.7011508942
>>> timeit.timeit('next((x for x in xrange(100) if L.append(x) and False), None)', 'L = []')
15.5235641003
>>> timeit.timeit('any(L.append(x) and False for x in xrange(100))', 'L = []')
20.9048290253
>>> timeit.timeit('filter(lambda x: L.append(x) and False, xrange(100))', 'L = []')
27.8524758816

Python 3:

>>> timeit.timeit('for x in range(100): L.append(x)', 'L = []')
13.719769178002025
>>> timeit.timeit('[x for x in range(100) if L.append(x) and False]', 'L = []')
15.041426660001889
>>> timeit.timeit('next((x for x in range(100) if L.append(x) and False), None)', 'L = []')
15.448063717998593
>>> timeit.timeit('any(L.append(x) and False for x in range(100))', 'L = []')
22.087335471998813
>>> timeit.timeit('next(filter(lambda x: L.append(x) and False, range(100)), None)', 'L = []')
36.72446593800123

Note that the time values are not that precise (for example, the relative performance of the first three options varied from run to run). My conclusion is that you should just use a loop, it's more readable and performs at least as well as the alternatives. If you want to avoid polluting the namespace, just del the variable after using it.