[Python-ideas] PEP-582 and multiple Python versions

Calvin Spealman cspealma at redhat.com
Mon Apr 1 08:26:08 EDT 2019

While the PEP does show the version number as part of the path to the
actual packages, implying support for multiple versions, this doesn't seem
to be spelled out in the actual text. Presumably __pypackages__/3.8/ might
sit beside __pypackages__/3.9/, etc. to keep future versions capable of
installing packages for each version, the way virtualenv today is bound to
one version of Python.

I'd like to raise a potential edge case that might be a problem, and likely
an increasingly common one: users with multiple installations of the *same*
version of Python. This is actually a common setup for Windows users who
use WSL, Microsoft's Linux-on-Windows solution, as you could have both the
Windows and Linux builds of a given Python version installed on the same
machine. The currently implied support for multiple versions would not be
able to separate these and could create problems if users pip install a
Windows binary package through Powershell and then try to run a script in
Bash from the same directory, causing the Linux version of Python to try to
use Windows python packages.

I'm not actually sure what the solution here is. Mostly I wanted to raise
the concern, because I'm very keen on WSL being a great entry path for new
developers and I want to make that a better experience, not a more
confusing one. Maybe that version number could include some other unique
identify, maybe based on Python's own executable. A hash maybe? I don't
know if anything like that already exists to uniquely identify a Python
build or installation.




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