Test if a number is prime in python

is_prime.py

# Taken from
# @see https://www.daniweb.com/programming/software-development/code/216880/check-if-a-number-is-a-prime-number-python
def is_prime(n):
    if n == 2 or n == 3: 
        return True
    elif n < 2 or n % 2 == 0: 
        return False
    elif n < 9:
        return True
    elif n % 3 == 0: 
        return False
    r = int(n**0.5)
    f = 5
    while f <= r:
        if n % f == 0 or n % (f + 2) == 0: 
            return False
        else:
            f += 6
    return True

def miller_rabin_isprime(a, i, n):
    """
    Miller-Rabin primality test
    returns a 1 if n is a prime
    usually i = n - 1
    does not test prime 2
    """
    if i == 0:
        return 1
    x = miller_rabin_isprime(a, i // 2, n)
    if x == 0:
        return 0
    y = (x * x) % n
    if ((y == 1) and (x != 1) and (x != (n - 1))):
        return 0
    if (i % 2) != 0:
        y = (a * y) % n
    return y