change return types to deal with upper bounds

[boanergies]

Have you checked closed issues? https://github.com/Textualize/textual/issues?q=is%3Aissue+is%3Aclosed

When using code like the example below and trying to run mypy on it

from textual.app import App, ComposeResult
from textual.widgets import OptionList


class ExampleApp(App):
    def compose(self) -> ComposeResult:
        yield OptionList("cool", "cool", id="watch")
        yield OptionList("to clear", id="update")

    async def on_option_list_option_selected(self, message: OptionList.OptionSelected):
        if message.option_list.id == "watch":
            option = self.query_one("#update")
            option.clear_options()


if __name__ == "__main__":
    app = ExampleApp()
    app.run()

you will then get this error:

example.py:13: error: "Widget" has no attribute "clear_options"  [attr-defined]
Found 1 error in 1 file (checked 1 source file)

This is because the return type for query_one should be a type with an upper bound. Another example explaining this type hint can be found here

It's probably not an immediate issue but it will make using mypy in textual projects better

[davep]

This would be the perfect time to use the expect_type parameter of query_one, for example:

option = self.query_one("#update", OptionList)

[boanergies]

Does using that argument somehow edit the return type of the type hint?

[davep]

Yes, see query_one in the source for he detail. Both this:

found = self.query_one(SomeWidget)

and

found = self.query_one("#some-query-here", SomeWidget)

will result in found being typed correctly.