code: def compare_string(self, expected_str, actual_str):
          
          if len(expected_str) != len(actual_str):
              return False
          result = 0
          for x, y in zip(expected_str, actual_str):
              result |= ord(x) ^ ord(y)
          return result == 0
docs: Returns True if the two strings are equal, False otherwise
          The time taken is independent of the number of characters that match
          For the sake of simplicity, this function executes in constant time only
          when the two strings have the same length. It short-circuits when they
          have different lengths