code: def _check_len(a, b):
      
      if len(a) != len(b):
          msg = "Length must be {}. Got {}".format(len(a), len(b))
          raise ValueError(msg)
docs: Raises an exception if the two values do not have the same
      length. This is useful for validating preconditions.
  
      :a: the first value
      :b: the second value
      :raises ValueError: if the sizes do not match