tox: `base_python` with full path fails with env name conflict

Issue

I’m not sure if I’m doing this right; I asked on StackOverflow a couple of days ago and got no reply.

This may be related to #2838, though that has been closed as fixed by #2840.

I have a set of test environments that test my code with different versions of Python, using environment names with py* factors (e.g., py3.8-pytest7). When I run my tests without an explicit base_python setting, they work fine, finding the correct versions of Python only because I’ve explicitly added all of them to my PATH environment variable.

I would prefer to explicitly specify paths to my various versions of Python, which are built with pythonz, rather than adding all of them to my PATH. For example:

[tox]
skip_missing_interpreters = false

[testenv]
base_python =
    py3.7: /home/cjs/.pythonz/pythons/CPython-3.7.17/bin/python3.7
    py3.8: /home/cjs/.pythonz/pythons/CPython-3.8.18/bin/python3
    py3.9: /home/cjs/.pythonz/pythons/CPython-3.9.18/bin/python

I have confirmed that the versions of Python above are what they look like:

$ /home/cjs/.pythonz/pythons/CPython-3.7.17/bin/python3.7 --version
Python 3.7.17
$ /home/cjs/.pythonz/pythons/CPython-3.8.18/bin/python3 --version
Python 3.8.18
$ /home/cjs/.pythonz/pythons/CPython-3.9.18/bin/python --version
Python 3.9.18

But when I try this, tox fails:

$ tox -vvv -r -e py3.7-pytest7,py3.8-pytest7,py3.9-pytest7
ROOT: 139 D setup logging to NOTSET on pid 606655 [tox/report.py:221]
py3.7-pytest7: 206 W remove tox env folder /home/cjs/co/public/gh/cynic-net/pytest_pt/.tox/py3.7-pytest7 [tox/tox_env/api.py:325]
py3.7-pytest7: 242 E failed with env name py3.7-pytest7 conflicting with base python /home/cjs/.pythonz/pythons/CPython-3.7.17/bin/python3.7 [tox/session/cmd/run/single.py:57]
py3.7-pytest7: FAIL ✖ in 0.04 seconds
py3.8-pytest7: 242 W remove tox env folder /home/cjs/co/public/gh/cynic-net/pytest_pt/.tox/py3.8-pytest7 [tox/tox_env/api.py:325]
py3.8-pytest7: 243 E failed with env name py3.8-pytest7 conflicting with base python /home/cjs/.pythonz/pythons/CPython-3.8.18/bin/python3 [tox/session/cmd/run/single.py:57]
py3.8-pytest7: FAIL ✖ in 0 seconds
py3.9-pytest7: 244 W remove tox env folder /home/cjs/co/public/gh/cynic-net/pytest_pt/.tox/py3.9-pytest7 [tox/tox_env/api.py:325]
py3.9-pytest7: 245 E failed with env name py3.9-pytest7 conflicting with base python /home/cjs/.pythonz/pythons/CPython-3.9.18/bin/python [tox/session/cmd/run/single.py:57]
  py3.7-pytest7: FAIL code 1 (0.04 seconds)
  py3.8-pytest7: FAIL code 1 (0.00 seconds)
  py3.9-pytest7: FAIL code 1 (0.00 seconds)
  evaluation failed :( (0.11 seconds)

Am I somehow specifying these wrong, or is this a bug?

Environment

• tox version 4.12.1
• Python 3.11.2 (for tox)

The test cases above were run from my pytest_pt project; that doesn’t have any other configuration that could be triggering the problem, as far as I can tell. However, I can probably cons up a smaller test case if necessary.