<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _check_len(a, b):
 """ 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 """

    if len(a) != len(b):
        msg = "Length must be {}. Got {}".format(len(a), len(b))
        raise ValueError(msg)