In a complement, we need to reverse the 1s to 0s and 0s to 1s. One of the best ways to do it is to xor the number with all 1s. **2**len(bin(num).lstrip('0b'))-1** gives the integer value of all 1s greater than the given number.

Here is the sample code.

```
class Solution(object):
def findComplement(self, num):
"""
:type num: int
:rtype: int
"""
return num^(2**len(bin(num).lstrip('0b'))-1)
```