Explanation for __pypackages__

[mrg0029]

I was very confused by this. I'd heard of __pypackages__/ before but not pyflow.

A Google search for "pyflow" found several other projects with the same name (the project that Python.gitignore was referring to didn't show up until the 5th result for me). I only figured it out after finding this PR.

__pypackages__ comes from this PEP. It's currently in draft status i.e. the proposal hasn't been accepted and the directory is not used within CPython.

I didn't know if pyflow's use of __pypackages__ was in conflict with the PEP or if it's trying to be some kind of early implementation of it. I'm guessing the latter since it mentions the PEP
in its readme.

tl;dr

The __pypackages__ directory isn't used by Python yet. But a somewhat obscure package is using the directory. It probably doesn't hurt to leave the ignore rule as is but a comment would be helpful.

[shiftkey]

cc @thedrow who added this in #3205 - does this make sense to you?

[mrg0029]

more research:

the big projects related to packaging and virtual environments

• Poetry had an issue about __pypackages__ here. A lot of +1s but no replies.
• Flit had zero matches when I searched its repo.
• Searching the whole github.com/pypa org found just this one comment.

less-widely used projects

• pipx, which I had heard of but never used, added this
• pythonloc, which I had not heard of but appears related to pipx, mentions it in their readme

[shiftkey]

Thanks @mrg0029 and @thedrow!