PIPX_DEFAULT_PYTHON not as flexible as --python

[pitrou]

Describe the bug

While --python allows flexible ways of specifying the desired interpreter (by version, by path...), the environment variable PIPX_DEFAULT_PYTHON only allows a full path to the Python executable.

How to reproduce

# export PIPX_DEFAULT_PYTHON=3.10
# pipx install xkcdpass
Traceback (most recent call last):
  File "/usr/local/bin/pipx", line 5, in <module>
    from pipx.main import cli
  File "/usr/local/lib/python3.8/site-packages/pipx/main.py", line 22, in <module>
    from pipx import commands, constants, paths
  File "/usr/local/lib/python3.8/site-packages/pipx/commands/__init__.py", line 2, in <module>
    from pipx.commands.environment import environment
  File "/usr/local/lib/python3.8/site-packages/pipx/commands/environment.py", line 6, in <module>
    from pipx.interpreter import DEFAULT_PYTHON
  File "/usr/local/lib/python3.8/site-packages/pipx/interpreter.py", line 183, in <module>
    DEFAULT_PYTHON = _get_absolute_python_interpreter(env_default_python)
  File "/usr/local/lib/python3.8/site-packages/pipx/interpreter.py", line 174, in _get_absolute_python_interpreter
    raise PipxError(f"Default python interpreter '{env_python}' is invalid.")
pipx.util.PipxError: Default python interpreter '3.10' is invalid.
# export PIPX_DEFAULT_PYTHON=
# pipx install --python=3.10 xkcdpass
⚠️ No executable for the provided Python version '3.10' found in PATH. Please make sure the provided version is on your PATH or the file path is valid. The
    provided version looks like a version, but both the python command and the Python Launcher were not found on PATH.

Expected behavior

# export PIPX_DEFAULT_PYTHON=3.10
# pipx install xkcdpass
⚠️ No executable for the provided Python version '3.10' found in PATH. Please make sure the provided version is on your PATH or the file path is valid. The
    provided version looks like a version, but both the python command and the Python Launcher were not found on PATH.

[uranusjr]

Personally I don’t think it is a good idea to set PIPX_DEFAULT_PYTHON to anything but a full path in the first place. The meaning of 3.10 (or anything but an absolute path) can change shifts underneath, and it is too much implicity. Of course the same applies to pipx install --python, but you need to explicitly opt into the implicity, and it only applies for one command.

[mcint]

Just pass the executable name or path, i.e. python3.10 or /usr/bin/python3.10, etc as appropriate for you.

Try PIPX_DEFAULT_PYTHON=python3.10 pipx install xkcdpass

Although pipx run -h does report either as usable,

--python PYTHON       Python to install with. Possible values can be the executable name (python3.11), the version to pass to py launcher
                      (3.11), or the full path to the executable.Requires Python 3.8 or above.

It looks like "python launcher", package py providing executable py (and genesis project of py.test / pytest), is in "maintenance mode", and lists most recent supported version of Python :: 3.10, per https://pypi.org/project/py/

$ pipx run --python=3.10 python3.10 -V
⚠️ No executable for the provided Python version '3.10' found in PATH. Please make sure the provided version is on your PATH or the file
    path is valid. The provided version looks like a version for Python Launcher, but `py` was not found on PATH.

https://github.com/pytest-dev/py
https://py.readthedocs.io/en/latest/

Just pass the executable name or path.

[pitrou]

@mcint Did you generate your response using ChatGPT? It does not seem to make sense at all.

[mcint]

I'm all ears if you want to meaningfully invite me to engage.

Sorry that adding context from my own brief poking around has proved inscrutably beneath engagement.

---

Am I mistaken in assuming "python launcher" that handles finding a python version when passed a version number is https://pypi.org/project/py/?

It seems that your request [support version-number-only specification] [additionally, when passed as an environment variable], is provided by a legacy library.

I would love to be corrected, and learn about better tools or other tools for managing python environment in succinct and easy ways.

[pitrou]

In case someone is reading this who is not a generative IA, answer to the question posted above:

Am I mistaken in assuming "python launcher" that handles finding a python version when passed a version number is https://pypi.org/project/py/?

Yes, you are. The Python launcher for Windows (py.exe) is actually provided by the standard installers:
https://docs.python.org/3/using/windows.html#launcher