Fix type hints for pipe using overloads. Fixes #355, #285

[dbrattli]

This PR fixes the typing issues with the pipe operator using typing overloads. The downside is that pylint does not support this yet and only sees the first overload (pylint-dev/pylint#2239). The good thing is that PyCharm does the right thing and see all the overloads and correctly infers the last type.

Thus I would rather do it the right way since PyCharm already supports this, and let pylint problems be pylint problems. This is similary to how the typing were fixed with typescript in RxJS (https://github.com/ReactiveX/rxjs/blob/master/src/internal/Observable.ts). Hopefully pylint will eventually be fixed.

[coveralls]

Coverage increased (+0.06%) to 92.6% when pulling 56bc897 on feature/pipe-typing into 1de2850 on master.

[dbrattli]

I really don't like that pylint handles this code so badly. I will try to see if I can disable it and only use mypy or try some other linter. Here is another pylint issue that tracks this problem pylint-dev/pylint#1581

[dbrattli]

The latest change with having an Observable specific pipe() overload first seems to make pylint happy, so now pylint, mypy and pyre are happy when you pipe your operators. Adding docstring to the first overload also make vscode happy when you inpect or auto-complete.

[jcafhe]

That looks good to me 👍

With a simple example:

x = rx.just(1).pipe(
    ops.map(lambda i: i),
    ops.to_future(),
    ops.map(lambda i:i),
    )

I've got a nice error with mypy:
pipe_typ.py:4: error: Argument 2 to "pipe" of "Observable" has incompatible type "Callable[[Observable], Future[Any]]"; expected "Callable[[Observable], Observable]"

Just a side note, to check a script which imports rx with mypy, I had to hack the setup.py and create an empty file py.typed. Basically, this just follows the procedure detailled in making-pep-561-compatible-packages. I'm not sure if this is 100% required, or if it's just me?

[dbrattli]

We should probably add py.typed. Didn't know about it so thanks for the link.

I btw started using Pyre today. Very nice type checking and integration with vscode: https://pyre-check.org/

[erikkemperman]

Looks good to me!

Coveralls reports slightly lower values, I think it is mostly due to the ellipses. Perhaps you can add something like the following to .coveragerc to make the build green.

...  # pylint: disable=pointless-statement

Or maybe without the comment. Approving regardless.