Idea: Allow installation of package local dependencies

[pradyunsg (Pradyun Gedam)]

The final post in Allowing Multiple Versions of Same Python Package in PYTHONPATH has the current state of affairs on this. Quoting myself:

@pradyunsg

It has been tried before. setuptools started out with multi version support, and, in some ways, that was the USP of it.

The tooling for this still exists in setuptools and is still documented at Multi-version installs — Python Packaging User Guide .

The thing is, this approach is somewhat incompatible with Python’s import mechanisms (there’s a single global import cache), causes subtle/difficult to reason about failures (see numpy example above, and think about how you’d debug a failure there — remember, repr and type aren’t going to include versions) and all the other things mentioned already.

Beyond that, I don’t think we’re contributing anything new to that discussion here.

And, yes, the new resolver is stricter which is why 20.3+ is going to be more painful. And, also, the older resolver still prints out that it installed with conflicts (see PR 5000 on pip).

Realistically, the only option you have if you really want to have conflicting dependencies is running pip with --no-deps, which opts out of all dependency resolution. That makes it clear that you’re opting into whatever solution for the dependency hell that you’ve determined works for you.