Implementing a "fallback"/shim package, similar to _distutils_hack

[amezin]

Recently, pytest started shipping a minimized version of py library as a module: https://github.com/pytest-dev/pytest/blob/main/src/py.py

The real, full py library is a package: https://github.com/pytest-dev/py

It works as expected, when everything is installed into virtualenv - if both pytest and the py library are installed, the package is preferred over the module, and import py loads the full library.

However, things go wrong when py is installed in system site-packages, and pytest is installed in a virtualenv. In this case, py module, not the package is loaded for import py, and plugins that depend on the full py library are breaking (pytest-dev/pytest#10451)

I started working on a solution: pytest-dev/pytest#10616 and found that it's quite similar to _distutils_hack here - except in pytest the finder needs to be added to the other end of meta_path.

I also see the "Please do not replicate this behavior." comment in setup.py. So I wonder: why? What are known downsides? Or is there maybe a better solution for my case?

Mentioning @jaraco @pganssle because of _distutils_hack git history.