Understanding the various interpreter locations

[ydirson]

1 month ago I started experimenting with hatch, and since then forgot all the details of what I did at the time. I had already noticed that hatch test -a only ran my tests for 3.10 and later (and at the time did not make the link with anything I would have done myself).

Now trying to make sense of all this, I start exploring hatch python, and find that despite 3.10-3.13 being run for my tests, hatch python show lists no python version as installed. Now:

$ hatch python install 3.10
Installed 3.10 @ /home/user/.local/share/hatch/pythons/3.10

... and sure enough there are no other versions there.

By inspecting running tests, I discover that the interpreters used, shown as .local/share/hatch/env/virtual/$PACKAGE/$SOME_ID/hatch-test.py3.13/bin/python3, with the executables symlinked into .local/share/hatch/env/virtual/.pythons/. Here I find 3.10, 3.12 and 3.13, with 3.11 being my system python (logically, it is the one symlinked from hatch-test.py3.11/bin/).

How did I find myself with those 2 sets of interpreters, one of which is not visible from hatch python?

[ydirson]

What's even stranger is that for the same project, a gitlab-ci build in a brand new container will run the tests for a different set of interpreters (3.11-3.13 here), and we can see for 3.12 (but not for the other ones) a line that seems to imply transparent installation of the python distribution:

Installing Python distribution: 3.12

A quick check of the container confirms that indeed in addition to 3.13 the container image does contain a system 3.11 from its Debian12 base:

$ podman run -it --rm python:3 /bin/bash -i
root@816a818bf0fc:/# which python3.11
/usr/bin/python3.11
root@816a818bf0fc:/# which python3.13
/usr/local/bin/python3.13

That explains part of the situation (notably that I did not remember installing those versions explicitly), now the remaining questions are:

• why do some versions trigger transparent auto-install of the distribution? Both the container and the dev box, showing different behaviours for 3.10, run Debian12, although one runs 3.13 by default)? That would not be "2 minor versions before I autoinstall, older I don't", right? :)
• why do they land in a location where hatch python does not see them?
• doesn't this "auto download" in some way defeat the apparent control given by hatch python?
• why this different handling of system interpreters?