Hi Arnar, Your two commands below aren't doing the same thing - one is doing a[i]*b[i] and the other is doing a[i]*b[j] for all i and j. As the second is harder, it takes longer.
Cheers, David On Fri, 2008-09-19 at 09:08 -0500, [EMAIL PROTECTED] wrote: > I think > [x*y for x in a for y in b] > feels pythonic, however it has a surprisingly lousy performance. > > In [30]: %timeit [ x * y for x,y in zip(a,b) ] > 100000 loops, best of 3: 3.96 ?s per loop > > In [31]: %timeit [ i*j for i in a for j in b ] > 100000 loops, best of 3: 6.53 ?s per loop > > In [32]: a = range(100) > > In [33]: b = range(100) > > In [34]: %timeit [ x * y for x,y in zip(a,b) ] > 10000 loops, best of 3: 51.9 ?s per loop > > In [35]: %timeit [ i*j for i in a for j in b ] > 100 loops, best of 3: 2.78 ms per loop > > Arnar -- ********************************** David M. Kaplan Charge de Recherche 1 Institut de Recherche pour le Developpement Centre de Recherche Halieutique Mediterraneenne et Tropicale av. Jean Monnet B.P. 171 34203 Sete cedex France Phone: +33 (0)4 99 57 32 27 Fax: +33 (0)4 99 57 32 95 http://www.ur097.ird.fr/team/dkaplan/index.html ********************************** _______________________________________________ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
