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
```