Fredrik Johansson wrote:
Consider sorting a list of pairs representing fractions. This can be
done easily in Python 2.x with the comparison function lambda
(p,q),(r,s): cmp(p*s, q*r). In Python 2.6, this is about 40 times
faster than using fractions.Fraction as a key function.
[steve@sylar ~]$ python2.7 -m timeit -s "L = [(1,2), (3,4), (0,5),
(9,100), (3,7), (2,8)]" "sorted(L, lambda (p,q),(r,s): cmp(p*s, q*r))"
10000 loops, best of 3: 25.1 usec per loop
[steve@sylar ~]$ python2.7 -m timeit -s "L = [(1,2), (3,4), (0,5),
(9,100), (3,7), (2,8)]" -s "from fractions import Fraction" "sorted(L,
key=lambda t: Fraction(*t))"
1000 loops, best of 3: 236 usec per loop
So for a short list, I get a factor of ten difference. For a longer
list, I'd expect the key function to win out. Much to my astonishment,
it doesn't -- I get similar results regardless of the size of L.
Size of L key/cmp
========== =========
6 9.4
600 13.9
60000 7.0
6000000 6.7
--
Steven
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