if num is power of 4, then it's square of a power of 2, so take square root, if it's power of 2, then it's true

```
def isPowerOfFour(self, num):
"""
:type num: int
:rtype: bool
"""
if num<1: return False #exclude negative numbers
if num**(1/2)%1!=0: return False #check whether is a qaure number
num=int(num**(1/2)) #take the square root
return not num&(num-1)
```