good example of imperative vs functional programming

fact.py

#!/usr/bin/env python3
from functools import reduce
import numpy as np

# mutable, imperative
def fact1(n):
    out = 1
    for i in range(1, n+1):
        out *= i
    return out


# functional, declarative
def fact2(n):
    return reduce(np.multiply, range(1, n+1))


assert( fact1(8) == fact2(8) )