I am trying to configure Pants for the Windows Subsystem for Linux. After doing a fresh Ubuntu install, discover that the default Python that has been automatically installed is Python 3.10.6. When I attempt to run Pants with this, I get:

No valid Python interpreter found. For `pants_version = "2.16.0.dev0"`, Pants requires Python 3.7, 3.8, or 3.9 to run. Please check that a valid interpreter is installed and on your $PATH.

From the docs, it appears that Pants will support builds with more recent versions of Python, but Pants itself cannot run with a version of Python newer than 3.9. So I install 3.9 following these instructions: https://www.debugpoint.com/install-python-3-11-ubuntu/ (substituting 3.9 instead of 3.11). I make 3.9 the default following those instructions:

bruce@groot:/mnt/c/git/semaphore-demo-python-pants$ sudo update-alternatives --config python3
There are 2 choices for the alternative python3 (providing /usr/bin/python3).

  Selection    Path                 Priority   Status
------------------------------------------------------------
  0            /usr/bin/python3.10   2         auto mode
  1            /usr/bin/python3.10   2         manual mode
* 2            /usr/bin/python3.9    1         manual mode

But when I try to run Pants I get:

bruce@groot:/mnt/c/git/semaphore-demo-python-pants$ pants test ::
Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 28, in <module>
    from CommandNotFound import CommandNotFound
  File "/usr/lib/python3/dist-packages/CommandNotFound/CommandNotFound.py", line 19, in <module>
    from CommandNotFound.db.db import SqliteDatabase
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 5, in <module>
    import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'

I try running the extra install command from here https://www.pantsbuild.org/docs/prerequisites#microsoft-windows:

bruce@groot:/mnt/c/git/semaphore-demo-python-pants$ sudo apt install unzip python3-dev python3-distutils python3-venv gcc
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
gcc is already the newest version (4:11.2.0-1ubuntu1).
python3-dev is already the newest version (3.10.6-1~22.04).
python3-distutils is already the newest version (3.10.6-1~22.04).
unzip is already the newest version (6.0-26ubuntu3.1).
python3-venv is already the newest version (3.10.6-1~22.04).
0 upgraded, 0 newly installed, 0 to remove and 20 not upgraded.

It seems like I missed a step or two somewhere...

So this:

bruce@groot:/mnt/c/git/semaphore-demo-python-pants$ pants test ::
Traceback (most recent call last):
  File "/usr/lib/command-not-found", line 28, in <module>
    from CommandNotFound import CommandNotFound
  File "/usr/lib/python3/dist-packages/CommandNotFound/CommandNotFound.py", line 19, in <module>
    from CommandNotFound.db.db import SqliteDatabase
  File "/usr/lib/python3/dist-packages/CommandNotFound/db/db.py", line 5, in <module>
    import apt_pkg
ModuleNotFoundError: No module named 'apt_pkg'

Looks to me like setting the default 3.9 using alternatives borked your system maybe and has ~nothing to do with Pants - a guess. I'd undo the alternatives bit. Pants just needs a Python 3.{7,8,9} to be visible on the PATH; that's all - it'll find it.