find gcd with recursion

def gcd(a,b):
    assert int(a) == a and int(b) == b, 'the number must be integer only ! '
    if a < 0 :
        a = -1 * a
    if b < 0 :
        b = -1 * b
    if b == 0 :
        return a 
    else :
        return gcd(b, a%b)

print(gcd(48, 12))