I have a python program defined by a function myFunc(m,n)

Basically, the function contains two for loops.

def myFunc(m, n) : for i in range(m) : for j in range(n) : # do it ...return 

I would like to calculate the time elapsed for m,n=20,20

I do it like this:

start_time = time.time()
b = myFunc(m,n)
elapsed_time = time.time() - start_time
print elapsed_time

The result is 0.0 almost always. Why?

Because time.time() - time.time() will be 0.0 when myFunc doesn't take very long.