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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 array_keys(self):
 """Return an iterator over member names for arrays only. Examples -------- ['baz', 'quux'] """

        for key in sorted(listdir(self._store, self._path)):
            path = self._key_prefix + key
            if contains_array(self._store, path):
                yield key