Interoperability of mojo Traits and Python protocols

[strangemonad]

I'm really excited to see the first pass of traits land in the language. I know there's still much to flesh out but one place that I think might be interesting to flesh out sooner rather than later is how traits and protocols are able to interoperate.

I feel like the python community is starting to converge and collectively understand the value of capturing interfaces as code rather than just documentation. Many popular libraries are exposing Protocols. There are also starting to be cross-project efforts like the dataframe interchange protocol https://data-apis.org/dataframe-protocol/latest/index.html. It's exciting to see this level of iterop maturity taking form in the python community given that most of the historical interop story has revolved around documenting and runtime checking the presence of certain fields and methods.

I think mojo could be a catalyst in continuing that discussion. The development of the mojo std lib might also benefit if it's grounded in a discussion around some minimal interoperability between traits and protocols (e.g. things like Stringable, Readable, Writable, Seekable, Sized, Countable...)

My open-ended question has 2 parts. I understand that traits and protocols are not 1-1 alike but it would be insightful to capture what aspects are meant to be compatible.

1. What's the plan / design for mojo to be able to consume existing python protocols? Should I expect to be able to use a protocol directly in place of a trait? Can I somehow define that a trait conforms to a protocol? I know this gets odd around things like fields and @property methods, maybe there's a subset of protocols, like function-only protocols, that a trait can conform to?
2. I know there's still a bunch to work out around exposing mojo native bindings back up to python, I'm not suggesting we solve that here. I think it would be useful to think about how trait's defined in mojo could be exposed and used in python more or less like protocols. This would allow a lot of the API and interface design work done by the mojo community to be exposed back out and used in python projects. A good prior here is both polars and pydantic core. They're both written in rust and use Py03 to expose well-defined traits as python types.