342. Power of Four

Given an integer (signed 32 bits), write a function to check whether it is a power of 4.

Example:
Given num = 16, return true. Given num = 5, return false.

Follow up: Could you solve it without loops/recursion?

Python:

class Solution(object):
def isPowerOfFour(self, num):
    """
    :type num: int
    :rtype: bool
    """
    if num <= 0:
        return False
    import math
    m = math.log(num, 4)
    return m == int(m)