There are at least two silly things in this code,

One is the hex conversion. Compare:

  >>> bin(int(binascii.hexlify(b"\x05"), 16))[2:]
  '101'

versus just:

  >>> bin(b"\x05"[0])[2:]
  '101'

Secondly, the code should just count the 1 bits; there is no need for a count of zeros.