190. Reverse Bits Leetcode Python

Reverse bits of a given 32 bits unsigned integer.
For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00111001011110000010100101000000).
Follow up: If this function is called many times, how would you optimize it?
Related problem: Reverse Integer

class Solution:
    # @param n, an integer
    # @return an integer
    def reverseBits(self, n):
        str='{0:032b}'.format(n)
        str=str[::-1]
        return int(str,2)