Building distributed systems in Python? Here is how python-cqrs tackles consistency with orchestrated sagas, the mediator pattern, and a transactional outbox—without preaching theory for ten pages first.

TL;DR

One thread through the code: place an order (command), read it back (query), then run a payment saga: close the invoice, credit the balance—without leaving half a payment applied.

After money is in, a transactional outbox carries a notification to other services (for example, “provision this VPS”) with at-least-once delivery to the bus; in-process domain events stay a different, in-memory contract (see the small table in part 3).

Transports and frameworks stay at the edge: nothing in a handler hard-codes HTTP, Kafka, or a CLI. More patterns (streaming, chain of responsibility, and the rest) live in the docs .

Links: GitHub · Docs · PyPI python-cqrs

A story in three crashes

A user places an order.…