Multiples of 3 and 5, http://projecteuler.net/problem=1, performance difference

multiple.py

#-*- coding:utf8 -*-

from __future__ import print_function

import sys
import time

if sys.version_info < (3,0):
    range = xrange


def f1(n=1000):
    return sum(range(3, n, 3)) + sum(range(5, n, 5)) - sum(range(15, n, 15))

def f2(n=1000):
    return sum((i for i in range(3, n) if i%3==0 and i%5==0))

def timeit(fn, args=None, n=1000):
    t0 = time.time()
    for i in range(0, n):
        fn(args)
    diff = time.time() - t0
    print("Done in %f s." % diff)


if __name__ == '__main__':
    timeit(f1, 100000)
    timeit(f2, 100000)

f1 is about as 10x fast as f2.