fix: adding py.typed file as marker for mypy

[Drezzerd]

What is this PR about?
This PR add a new file py.typed at the root of the module to fix this issue
The goal is to allow mypy analyze

Checklist

• Explain important implementation details 👆
• Make sure that the pre-commit linting/style checks pass.
• Link relevant issues (preferably in nice commit messages)
• Are the changes covered by tests and docstrings?
• Fill out the short summary sections 👇

Major / Breaking Changes

• None

New features

• Enable mypy type analysis
• Fixes mypy error message

Bugfixes

• my_file.py:1: error: Skipping analyzing “pymc”: module is installed, but missing library stubs or py.typed marker [import-untyped]

Documentation

• PEP 561
• mypy docs

Maintenance

• None

---

📚 Documentation preview 📚: https://pymc--7008.org.readthedocs.build/en/7008/

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[thomasaarholt]

The pyright docs also make it clear that a package that does type hinting (it doesn't need to be fully typed, or even correctly typed), should have a py.typed file in the root module directory.

This PR makes sense.

[maresb]

py.typed should go in the package root, not the project root. (Just pushed a commit to fix.)

[maresb]

Our typing seems very rudimentary to me, so I wonder if doing this will lead to more chaos than it solves.

Out of curiosity I checked the situation with scipy, and they still don't have a py.typed file yet. They added one in scipy/scipy#11946 and removed in in scipy/scipy#12210 shortly after. However, the removal doesn't seem associated with any particular complaint.

[maresb]

@michaelosthege, could you explain what this is for? It seems to be unused.

pymc/scripts/run_mypy.py

Lines 53 to 61 in 05b557f

	def enforce_pep561(module_name):
	try:
	module = importlib.import_module(module_name)
	fp = pathlib.Path(module.__path__[0], "py.typed")
	if not fp.exists():
	fp.touch()
	except ModuleNotFoundError:
	print(f"Can't enforce PEP 561 for {module_name} because it is not installed.")
	return

[lucianopaz]

I'm confused with the PEP. It says that we need to include the py.typed file as a package data in pyproject.toml, but maybe this is not necessary thanks to this?

[maresb]

@lucianopaz I think it's included due to setuptools-scm. I verified that it's included in both sdist and wheels.

[maresb]

Ah, no, we're not using setuptools-scm. In any case I verified that it's included.

[michaelosthege]

The enforce_pep561 was a hack to add a py.typed to Aesara back in the day when the Aesara devs categorically refused to add py.typed until type hints were flawless.
We used this to already start working on improving PyMC type hints.

Meanwhile, PyTensor has the py.typed marker so the hack can safely be removed 👍

[maresb]

Thanks a lot @michaelosthege for the context! Seems like you already have some experience with py.typed. Do you see any potential disadvantages to enabling?

I'm assuming that users who are using pymc as a library may see a bunch of new type errors, but the main userbase is probably people writing notebooks who just want their IDEs to give type hints, so the benefits will greatly outweigh the downsides. Does this seem like an accurate assessment?

[michaelosthege]

Thanks a lot @michaelosthege for the context! Seems like you already have some experience with py.typed. Do you see any potential disadvantages to enabling?

I'm assuming that users who are using pymc as a library may see a bunch of new type errors, but the main userbase is probably people writing notebooks who just want their IDEs to give type hints, so the benefits will greatly outweigh the downsides. Does this seem like an accurate assessment?

I'll have to try this myself in one project with a rather involved model. If you check the mypy logs, we still have a bunch (>100?) errors that get ignored and many of those are due to function dispatching method overloading and PyMCs abuse of __new__ in the distribution API.

95 % of user interaction with the PyMC API goes through the distribution API (which totally breaks mypy and IDEs) and another 4 % is via pm.sample* which is trivial w.r.t. type hints.

@thomasaarholt did you try a real-world project with py.typed enabled?