Declare function output #359

Hello,

Assume a function:
`def function1(x, y):
z = x+y
return z'

I would normally invoke it like so:
result = function1(10, 50)
and I can use result for subsequent computations.

But let's say I want to profile the memory usage and invoke it like so:
mem_usage = memory_usage((function1, (10,50, )))

The code returns the correct memory usage, but there is no way I can declare an output variable for the function so that I can use it in subsequent steps.