OnPressHandler.__call__() returns object, but which value?

[jbrains]

I notice that OnPressHandler.__call__() returns object, but the documentation doesn't say what value the framework expects it to return. Anything? None?

[rmartin16]

A return type of object is the same as a return type of Any insofar as the return type can be anything in Python. The difference is that type checkers allow any operation on Any return types while only operations that all are valid for all objects can be used for object return types. Mypy has more thoughts on this.

The intention here is to avoid proliferating Any return types in to user code.

[freakboy3742]

Ah - ok - this is more of a case where from a strict documentation perspective, the return type is None, but from a "we want to allow an arbitrary function that might return a value" to not be rejected by strict typecheckers.

That makes sense; in which case, adding documentation as you note would make sense - as would a corresponding FAQ entry for "why do all the handlers have a type annotation of object, but are documented as 'return value ignored'"?

[mhsmith]

it prevents an arbitrary function as the handler from satisfying type checking

Only developers who enable type checking would be affected by this, but they're exactly the kind of developer who'd prefer that we were strict about function return type hints. So I think None is more useful here.

None would also produce much clearer documentation than having to write "any object, but actually we ignore it" on every event handler.

[jbrains]

Adding to that The return value is ignored. may sufficiently help clarify this behavior.

Indeed, this would have been good enough for me in this particular situation. I mostly wanted to know whether I was missing something, and it's clear now that I wasn't. Thank you!

[freakboy3742]

Only developers who enable type checking would be affected by this, but they're exactly the kind of developer who'd prefer that we were strict about function return type hints.

I don't know that this is necessarily true. My observation is that a lot of the reports we've had of typing issues don't come from MyPy/PyRight/ty users, but from PyCharm users complaining about "the squiggly lines in their IDE".

I'll grant those users are less likely to be pushing the "Any function as a handler" approach, though.

[mhsmith]

I think we're in agreement that something needs to be changed here, so let's convert this into an issue: #3582.