Can I reasonably use mypy in a Reflex project?

[luator]

I'm working on a project with Reflex. In the past, we had not much problems using mypy but since upgrading Reflex from 0.6.4 to the latest release (now 0.7.5), mypy suddenly has lots of complains.

Many of these issues seem to be coming from within Reflex. For example, the automagically created setters for state variables seem to be unknown to mypy. Further, I got complains like "Module not callable" on rx.icon() or '"Var[Any]" has no attribute "button"' on rx.color_mode.button().

Now I'm wondering: Are others using mypy on Reflex projects without problems (i.e. those are issues I could actually fix in my code) or is this an inherent problem with Reflex and should I just give up on using mypy in this project?

[luator]

I stumbled upon another weird Reflex pattern mypy complains about: I have code similar to this snippet from the docs for handling uploaded files:

class State(rx.State):
    """The app state."""

    async def handle_upload(
        self, files: list[rx.UploadFile]
    ):
        ...


def index():
    return rx.vstack(
        rx.upload(
            ...,
            on_drop=State.handle_upload(
                rx.upload_files(upload_id="upload2")
            ),
        ),
        ...,
    )

mypy errors are

error: Missing positional argument "files" in call to "handle_upload" of "State" [call-arg]
error: Argument 1 to "handle_upload" of "State" has incompatible type "FileUpload"; expected "State" [arg-type]

Both of these errors make complete sense to me. At this point, I'm wondering how/why this is actually working at runtime. I guess some black magic in the Reflex internals?

[masenf]

if you decorate the event handler with @rx.event is the error still there?

As for the autogenerated setters, i don't know if there's a way we can actually statically type those because they're dynamic runtime names.

[luator]

Thanks for the hint. The two errors quoted above go away but there is now a new one:

error: "EventCallback?[Any]" not callable [misc]

A bit off topic but out of curiosity: How does this actually work? The decorator can obviously do something but even without it, the code was working, even though it looks wrong when reading the code (calling a function with one argument, that requires two).

[masenf]

the decorator is for typing hints only, it's just a passthrough that captures the event handler signature in a generic typevar

[luator]

Is the new error, I'm getting now expected?

Generally, what is the recommended procedure with mypy? I guess I simply need to # type:ignore all unfixable errors (like the generated setters and similar issues)?

[adhami3310]

we don't particularly support mypy out of sanity, we have a gigantic API that is pretty hard to make it type check correctly for mypy and pyright, some stuff are just limitations/bugs of mypy, we welcome PRs though

[luator]

Do I interpret your response correctly that pyright should work better with Reflex? I never used it before, but would be willing to switch if it improves things.

[adhami3310]

Do I interpret your response correctly that pyright should work better with Reflex? I never used it before, but would be willing to switch if it improves things.

Pyright is what we use inside of our CI and internally. It should work better but it's not without its limitations.

[luator]

Thanks, I'll give it a try.