def close(self):
		'''关闭与数据库的连接'''
		if VERBOSE:
			print 'Database connection CLOSE.'
		self.conn.close()
def __enter__(self):
        entering = not transaction_states[self.using]
        transaction_states[self.using].begin()
        self._no_monkey.__enter__(self)
        if entering:
            on_commit(transaction_states[self.using].commit, self.using)