def registerProducer(self, producer, streaming):
        """
        Register to receive data from a producer.

        This sets this selectable to be a consumer for a producer.  When this
        selectable runs out of data on a write() call, it will ask the producer
        to resumeProducing(). When the FileDescriptor's internal data buffer is
        filled, it will ask the producer to pauseProducing(). If the connection
        is lost, FileDescriptor calls producer's stopProducing() method.

        If streaming is true, the producer should provide the IPushProducer
        interface. Otherwise, it is assumed that producer provides the
        IPullProducer interface. In this case, the producer won't be asked to
        pauseProducing(), but it has to be careful to write() data only when its
        resumeProducing() method is called.
        """
        if self.producer is not None:
            raise RuntimeError(
                "Cannot register producer %s, because producer %s was never "
                "unregistered." % (producer, self.producer))
        if self.disconnected:
            producer.stopProducing()
        else:
            self.producer = producer
            self.streamingProducer = streaming
            if not streaming:
                producer.resumeProducing()

        Register to receive data from a producer.

        This sets this selectable to be a consumer for a producer.  When this
        selectable runs out of data on a write() call, it will ask the producer
        to resumeProducing(). When the FileDescriptor's internal data buffer is
        filled, it will ask the producer to pauseProducing(). If the connection
        is lost, FileDescriptor calls producer's stopProducing() method.

        If streaming is true, the producer should provide the IPushProducer
        interface. Otherwise, it is assumed that producer provides the
        IPullProducer interface. In this case, the producer won't be asked to
        pauseProducing(), but it has to be careful to write() data only when its
        resumeProducing() method is called.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/abstract.py