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?