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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 _hashed_indexing_key(self, key):
 """ validate and return the hash for the provided key *this is internal for use for the cython routines* Parameters key : string or tuple Returns ------- np.uint64 Notes ----- we need to stringify if we have mixed levels """

        from pandas.core.util.hashing import hash_tuples, hash_tuple

        if not isinstance(key, tuple):
            return hash_tuples(key)

        if not len(key) == self.nlevels:
            raise KeyError

        def f(k, stringify):
            if stringify and not isinstance(k, str):
                k = str(k)
            return k
        key = tuple(f(k, stringify)
                    for k, stringify in zip(key, self._have_mixed_levels))
        return hash_tuple(key)