Question: How can I get transit serialized (as msgpack) bytes to pass to a specialized "writer"?

[dcj]

I'd like to serialize Kafka values as (msgpack) transit.

The python-kafka kafka.KafkaProducer takes:

value_serializer (callable) – used to convert user-supplied message values to bytes. If not None, called as f(value), should return bytes. Default: None.

Is there a way to get the serialized bytes from transit-python, or are serialization and writing combined/complected?