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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 _recv_flow(self, method_frame):
        '''
        Receive a flow control command from the broker
        '''
        self.channel._active = method_frame.args.read_bit()

        args = Writer()
        args.write_bit(self.channel.active)
        self.send_frame(MethodFrame(self.channel_id, 20, 21, args))

        if self._flow_control_cb is not None:
            self._flow_control_cb()