Question

Which one’s a better way of doing list comprehension in python (in terms of computation time & cpu cycles).
In example (1) is the value f(r) evaluated in each iteration or is it evaluated once and cached ?

1. y = [x*f(r) for x in xlist]

2. c = f(r)

   y = [x*c for x in xlist]

where

def f(r):
    ... some arbitrary function ...

Answer 1

I would probably choose the latter because the Python compiler doesn’t know if the function has side-effects so it is called for each element.