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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 drop_all(self, checkfirst: bool = True) -> None: """Drop all data, tables, and databases for the PyBEL cache. :param checkfirst: Check if the database exists before trying to drop it """

        self.session.close()
        self.base.metadata.drop_all(bind=self.engine, checkfirst=checkfirst)