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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 schema(self):
 """return the schema instance if this is reference to another table"""

        if not hasattr(self, "_schema"):
            ret = None
            o = self._type
            if isinstance(o, type):
                ret = getattr(o, "schema", None)

            elif isinstance(o, Schema):
                ret = o

            else:
                module, klass = utils.get_objects(o)
                ret = klass.schema

            self._schema = ret

        return self._schema