The log base 4 of num is only integral when num is a power of four.
Given any log function you can calculate log base b of n by log(n)/log(b). This is floating point math using a (probably?) slow math function. (Pulling log4 out as a separate function also has significant overhead In Python)
Leetcode didn't give me my performance stats because there had not been enough submissions...
from math import log l4 = log(4) def log4(n): return log(n)/l4 class Solution(object): def isPowerOfFour(self, num): if num <= 0: return False return log4(num)%1 == 0