input: from typing import List
  
  def bitwise_xor(s1: str, s2: str) -> str:
      """ Takes two binary strings s1 and s2 made up of 0s and 1s.
      Executes a binary XOR operation on these strings and returns the output as a string.
      >>> bitwise_xor('010', '110')
      '100'
      """
output:     return ''.join('1' if b1 != b2 else '0' for b1, b2 in zip(s1, s2))