modExp (Python)

# b^n (mod m)
def modExp(b, n, m):
    binary = format(n, "0b")
    result = 1

    # Update b if it is more than or equal to m
    b = b % m

    if (b == 0):
        return 0

    binary = str(binary)[::-1]

    for i in range(len(binary)):
        if (binary[i] == "1"):
            result = (result * b) % m
        b = (b * b) % m

    return result