Add PEP 561 Compatiblity

[harens]

Hi there 👋

I just saw #39 and thought it might be useful to add a py.typed file. This allows downstream projects to use the type hints for things like PyCharm, mypy, pytype etc.

Without this file, mypy currently complains in projects that use rich-click:

error: Skipping analyzing "rich_click": module is installed, but missing library stubs or py.typed marker

The py.typed file makes rich-click PEP-561 compatible, and allows the inline types to be used. See here for further explanation.

[ewels]

Nice! Yeah, @Jorricks has been helping with this as I am new to Python typing.. 👴🏻

Should we be running mypy with GitHub Actions to check for errors in the typing?

[Jorricks]

Oh that's a good pointer! I never created such a file.
Let's add it indeed.

Regarding running MyPy, that's included in the pre-commit. I'll continue working on that tomorrow.

[harens]

Thank you @ewels for merging, and thanks @Jorricks for your effort on the typing front. 👍 I know from experience just how much work that can be, so I really appreciate what you're doing.

Should we be running mypy with GitHub Actions to check for errors in the typing?

Regarding running MyPy, that's included in the pre-commit.

Do you trust that the developer will always install the pre commit? ;)

As for mypy in general, I'd say it's quite a double-edged sword. It's saved me from mistakes in the past, but it takes a lot of effort to squash out errors from mypy, let alone mypy --strict. You might prefer the beartype approach of checking types at runtime:

From @leycec:

You want to write code rather than fight a static type checker, because static type inference of a dynamically-typed language is guaranteed to fail and frequently does. If you've ever cursed the sky after suffixing working code incorrectly typed by mypy with non-portable vendor-specific pragmas like # type: ignore[{unreadable_error}], beartype was written for you.

[ewels]

Do you trust that the developer will always install the pre commit? ;)

The GitHub Actions CI workflow runs the pre-commit checks, so they don't need to - the PR checks will fail if it doesn't validate. See #40

[Jorricks]

Well in my opinion, MyPy is indeed a tiny bit annoying but it prevents so many bugs.
Furthermore, it makes sure you are set up for success around None values. And so much more.. I always felt it is worth the extra effort.

[ewels]

Bit late now, but maybe we could put this into setup.cfg instead? Most stuff is in there, it's only the requirements that are in setup.py so that they can be picked up by GitHub:

rich-click/setup.cfg

Line 39 in 6d444bf

# Dependencies are in setup.py for GitHub's dependency graph.

I assume it would still work if in the .cfg file instead?