reverse integer bits in binary

reverse_bits.py

import math


class Solution:
    def reverseBits(self, bin_int):
        '''
        :type bin_int: int
        :rtype: int
        '''
        if bin_int <= 1: return bin_int

        bit_size = bin_int.bit_length()
        start = 1
        res = None
        lsb = None
        for each_shift in range(bit_size):
            # print(res, bin_int)
            lsb = (bin_int & 1)
            if res == None:
                res = lsb
            else:
                res <<= 1
                res |= lsb
            bin_int >>= 1
        return res