input: from typing import List
  
  
  def string_xor(a: str, b: str) -> str:
      """ Input are two strings a and b consisting only of 1s and 0s.
      Perform binary XOR on these inputs and return result also as a string.
      >>> string_xor('010', '110')
      '100'
      """
  
output:     result = []
      for i in range(len(a)):
          if a[i] == b[i]:
              result.append('0')
          else:
              result.append('1')
      return ''.join(result)