Python：为什么`lambda` 比函数或乘法快？

Question

Doing simple multiplication seem that lambda is faster; why?

import numpy as np
import time

def mult(x=None, y=None): return x*y

x = np.random.rand(10000,10000)

f = lambda z, g: z*g

start = []
end = []

for i in xrange(100):
    start.append(time.time())
    x*5
    end.append(time.time())

start = np.array(start)
end = np.array(end)

print np.sum(end-start)/len(end)

start = []
end = []

for i in xrange(100):

    start.append(time.time())
    f(x, 5)
    end.append(time.time())

start = np.array(start)
end = np.array(end)

print np.sum(end-start)/len(end)

start = []
end = []

for i in xrange(100):

    start.append(time.time())
    mult(x, 5)
    end.append(time.time())

start = np.array(start)
end = np.array(end)

print np.sum(end-start)/len(end)

I get:

0.487183141708
0.482636857033
0.483230319023

Answer 1

Use timeit module:

import numpy as np

def mult(x=None, y=None):
    return x*y
x = np.random.rand(1000, 1000)
f = lambda z, g: z*g


if __name__ == '__main__':
    import timeit
    setup_str = "from __main__ import x, f, mult"
    print(timeit.timeit('x*5', number=100, setup=setup_str))
    print(timeit.timeit('f(x, 5)', number=100, setup=setup_str))
    print(timeit.timeit('mult(x, 5)', number=100, setup=setup_str))

Output

0.3345440280099865

0.42724098000326194

0.3455269880068954