code: def xor(left, right):
      
      maxlength = max(map(len, (left, right)))
  
      ileft = string_to_int(rpad(left, maxlength))
      iright = string_to_int(rpad(right, maxlength))
      xored = ileft ^ iright
      return int_to_string(xored)
docs: xor 2 strings. They can be shorter than each other, in which case
      the shortest will be padded with null bytes at its right.
  
      :param left: a string to be the left side of the xor
      :param right: a string to be the left side of the xor