Is there a best practice to make a package PEP-561 compliant?

Question

I'm writing a Python project which is published as a package to a pypi-like repository (using setuptools and twine). I use type hints in my code.

The issue is, when importing the package from a different project and running mypy, I get the following error: error: Skipping analyzing 'XXX': found module but no type hints or library stubs

As I understand, I got this error because my package was not compliant with https://www.python.org/dev/peps/pep-0561/ .

After some searching online, I didn't find a way that was not manual to add the required files to the package.

I resorted to writing my own code to:

1. Run stubgen to create stub files.
2. Create py.typed files in every directory.
3. Collect all the created files in a dict in package_data field in the setup.py file.

This code solved the issue and mypy runs without errors. But this feels very wrong to me. Is there a standard tool for making a package PEP-561 compliant? Am I missing something else?

Answer 1

As mentioned before, You need to add the py.typed in the package folder of the module. You also need to add that file to the setup.py package_data - otherwise the file would not be part of the package when You deploy it.

I personally put the type annotations in the code and dont create extra stub files - but that is only possible from python 3.4 upwards. If You want to make python2.7 compatible code, You can not use inline type annotation - in that case You can use stub files.

If You want to type annotate a third party library, You can write a *.pyi file for the functions You use for that library. That can be a bit tricky, because MYPY must only find that *.pyi file ONCE in the MYPY Path.

So I handle it that way :

for local testing, the MYPY path is set to a directory were I collect all the 3rd party stubs, for testing on travis, I have a subdirectory in the package with the stubs needed for that module to test it on travis, and set the mypy path accordingly.