Add py.typed file to package

[thomashopkins32]

Description

Add py.typed marker for the package.

Motivation and Context

When using ophyd-async, the mypy extension in VS Code complains that there is no py.typed stub in event-model.

How Has This Been Tested?

[evalott100]

This breaks bluesky's tox -e type-checking. There should probably be a PR there to fix?

[thomashopkins32]

@evalott100 Ah I'm guessing because bluesky has typing errors related to event-model objects?

[evalott100]

Ah I'm guessing because bluesky has typing errors related to event-model objects?

It's because we have some TypedDict e.g datum_doc which we know is Datum, but type checking sees as some union of documents because it comes from a structure typed as such.

https://github.com/bluesky/bluesky/blob/ca4f8aa136c91dccd428936d2d0ebe963b925f4e/src/bluesky/callbacks/tiled_writer.py#L197-L202

Here _docs_cache values are typed as Datum | Resource | StreamResource so you get key errors on "datum_id" for those possibilities. I would see if you can clean up the typing, though I think most of these need to be handled with casting, i.e

                    datum_doc = typing.cast(Datum, self._docs_cache.pop(datum_id))

since there's no way the type checker will know that an element with uid datum_id has to be a Datum.

I think this is the format of most of the issues with type checking on bluesky for this PR.

[thomashopkins32]

Okay, I'll try to take a stab at it and see if I can get it to work. Thanks for the info!

[evalott100]

Okay, I'll try to take a stab at it and see if I can get it to work. Thanks for the info!

Cheers!

Instead of casting, the above example can probably be solved by making individual _datum_docs_cache, _stream_resource_docs_cache and _resource_docs_cache, then adding to the respective cache in these:

https://github.com/bluesky/bluesky/blob/ca4f8aa136c91dccd428936d2d0ebe963b925f4e/src/bluesky/callbacks/tiled_writer.py#L212-L219

This would be nicer, and actually lead to better code across the file imo.

For some places you might have to cast instead though. If there's somewhere where a nicer typing solution is feasible but you don't have the time then just adding casts for now is probably fine.