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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _check_key(self, key):
 """ Ensures well-formedness of a key. """

        if not len(key) == 2:
            raise TypeError('invalid key: %r' % key)
        elif key[1] not in TYPES:
            raise TypeError('invalid datatype: %s' % key[1])