[Python-Dev] PEP-582 and multiple Python installations (original) (raw)

Calvin Spealman cspealma at redhat.com
Tue Apr 2 11:17:20 EDT 2019

(I originally posted this to python-ideas, where I was told none of this PEP's authors subscribe so probably no one will see it there, so I'm posting it here to raise the issue where it can get seen and hopefully discussed)

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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CALVIN SPEALMAN

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