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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 catalog(self):
 """Interface through which the user may create, drop, alter or query underlying databases, tables, functions etc. :return: :class:`Catalog` """

        from pyspark.sql.catalog import Catalog
        if not hasattr(self, "_catalog"):
            self._catalog = Catalog(self)
        return self._catalog