🏷️ Adding Type Annotations

[YousefEZ]

Request:

• adding type Annotations to the function signatures,
• add the py.typed marker so that other packages can type check against the type annotations

[mentalisttraceur]

Cheers!

My current plan is to release type hints for compose in a secondary stub-only package.

I'm not sure how soon I'll get to it, and there are some tricky things to figure out. (I wrote a little bit more on that in the comments of this StackOverflow question.)

[mentalisttraceur]

So here's the situation when I last looked into it:

Problem: there's no way to do just one type-hint for variadic compose. We have to do type hint overloads for each arity, like this:

from typing import Callable, TypeVar, ParamSpec, overload

P = ParamSpec('P')
R1 = TypeVar('R1')
R2 = TypeVar('R2')
R3 = TypeVar('R3')
R4 = TypeVar('R4')
@overload
def compose(f2: Callable[[R1], R2], f1: Callable[P, R1]) -> Callable[P, R2]:
    ...
@overload
def compose(f3: Callable[[R2], R3], f2: Callable[[R1], R2], f1: Callable[P, R1]) -> Callable[P, R3]:
    ...
@overload
def compose(f4: Callable[[R3], R4], f3: Callable[[R2], R3], f2: Callable[[R1], R2], f1: Callable[P, R1]) -> Callable[P, R4]:
    ...
# and so on, up to some large number

When I last tried that, it seemed that MyPy had issues with typing.overload in the same file as the code; I haven't yet gotten around to testing it in a separate typing stub file, but if that works then that might be the best we can do.

(I'm hoping that the above type-hint overloads work well enough for most cases despite compose/acompose/sacompose being classes with callable instances - a more precise solution would be to type-hint __init__ and __call__ in a way that links the types between them, assuming the existing type hint stuff can even handle that.)

[mentalisttraceur]

Finally got around to sitting down and trying the typing stubs package approach. It works!

Confirmed with MyPy, Pyre, and Pyright.

[mentalisttraceur]

Implemented in compose-stubs, about as well as it can be.

I'll promote the stubs to stable v1 release (and push out a compose release with the description updated to mention the stubs package) soon unless someone catches a serious problem that I missed.

[mentalisttraceur]

Okay, compose-stubs is now officially released as v1.0.0, and compose v1.5.0 now officially points to it in the package description and repo README. 🎉