Do more imported objects affect performance
nick at craig-wood.com
Mon Dec 1 12:30:44 CET 2008
Rafe <rafesacks at gmail.com> wrote:
> On Dec 1, 7:26?am, "Filip Gruszczy?ski" <grusz... at gmail.com> wrote:
> > I have following question: if I use
> > from module import *
> > instead
> > from module import Class
> > am I affecting performance of my program? I believe, that all those
> > names must be stored somewhere, when they are imported and then
> > browsed when one of them is called. So am I putting a lot of "garbage"
> > to this storage and make those searches longer?
> Why use it if you don't need it? Your post implies a choice and the
> '*' import can really make things muddy if it isn't actually necessary
> (rare). Why not just import the module and use what you need? It is
> way easier to read/debug and maintains the name-space.
Importing the module is actualy slower... If you import the name into
your namespace then there is only one lookup to do. If you import the
module there are two.
$ python -m timeit -s 'from timeit import Timer' 'Timer'
10000000 loops, best of 3: 0.0784 usec per loop
$ python -m timeit -s 'import timeit' 'timeit.Timer'
1000000 loops, best of 3: 0.243 usec per loop
I'm not suggestion you should ever use "from module import *" only
ever import the things you actually need, eg
"from module import MyClass, my_function"
And here is the test again, actually calling something with the same
difference in execution speed :-
$ python -m timeit -s 'from os import nice' 'nice(0)'
1000000 loops, best of 3: 1.21 usec per loop
$ python -m timeit -s 'import os' 'os.nice(0)'
1000000 loops, best of 3: 1.48 usec per loop
Nick Craig-Wood <nick at craig-wood.com> -- http://www.craig-wood.com/nick
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