Greatest Common Divisor (Python)

gcd.py

#! /usr/bin/python

# Greatest Common Divisor in python


# recursive (as given)
def gcd_r(a, b):
    if b == 0:
        return a

    return gcd(b, a % b)


# iterative: more efficient
# This is due to not requiring to traverse the stack and the better
# use of the cpu cache in a loop (although for such a small code
# snippet this difference can be minimal)
def gcd(a, b):
    while b != 0:
        a, b = b, a % b

    return a


if __name__ == '__main__':
    # Testing input values
    assert gcd(5, 3) == gcd(3, 5) == 1
    assert gcd(10, 5) == gcd(5, 10) == 5
    assert gcd(1, 0) == gcd(0, 1) == 1
    assert gcd(10, 7) == gcd(7, 10) == 1
    assert gcd(8, 12) == gcd(12, 8) == 4
    assert gcd(21, 15) == gcd(15, 21) == 3
    assert gcd(27, 27) == 27

    assert gcd(10, 24) == 2
    assert gcd(1000, 80) == 40
    assert gcd(10000000, 86) == 2