Asyncio Coroutine Support

If you’re using asyncio coroutines in Python 3.5 or later (async def yourcoro() and await yourcoro()) together with Eliot, you need to run the following before doing any logging:

import eliot
eliot.use_asyncio_context()

Why you need to do this

By default Eliot provides a different “context” for each thread. That is how with start_action(action_type='my_action'): works: it records the current action on this context.

When using coroutines you end up with the same context being used with different coroutines, since they share the same thread. Calling eliot.use_asyncio_context() makes sure each coroutine gets its own context, so with start_action() in one coroutine doesn’t interfere with another.

However, Eliot will do the right thing for nested coroutines. Specifically, coroutines called via await a_coroutine() will inherit the logging context from the calling coroutine.

Limitations

• I haven’t tested the Python 3.4 yield from variation.
• This doesn’t support other event loops (Curio, Trio, Tornado, etc.). If you want these supported please file an issue: https://github.com/ScatterHQ/eliot/issues/new There is talk of adding the concept of a coroutine context to Python 3.7 or perhaps 3.8, in which case it will be easier to automatically support all frameworks.