input: from typing import List
  
  def binary_xor(s1: str, s2: str) -> str:
      """ Take two binary strings s1 and s2 only composed of 1s and 0s.
      Compute their binary XOR and return the result as a string.
      >>> binary_xor('010', '110')
      '100'
      """
output:     
      result = []
      for bit1, bit2 in zip(s1, s2):
          result.append('1' if bit1 != bit2 else '0')
      return ''.join(result)
  