The previous discussions on this:
- Idea: Allow installation of package local dependencies
- Allowing Multiple Versions of Same Python Package in PYTHONPATH
The issue isn’t to do with pip, Python does not support this.
You can read there, but one classic problem is, say you had two versions of numpy installed, and they implemented ndarray differently in memory, when you (or libraries you installed) pass an ndarray around, and it ends up being created by one version of numpy and used by a different version so of numpy, it could crash or read the data wrong.