Skip python.exe with uv install python --default

[Vynce]

I love the uv python install --default feature (#8650), but it creates a python.exe executable in addition to a python3.exe executable. Unfortunately, we still need python.exe to resolve to a Python 2.7 interpreter for the time being. Would you be willing to add a uv.toml setting or an alternative --default-py3only arg or something that limits the feature to only managing python3.exe. Similar issue on Linux, but I'm specifically looking at the Windows behavior.

[zanieb]

Oof. Hm.. I guess a uv.toml setting is less controversial to me (it seems niche for the CLI), but we don't have Python install settings there yet.

Would an environment variable be sufficient?

Unfortunately, we still need python.exe to resolve to a Python 2.7 interpreter for the time being.

Would it be feasible to specify the full path to your 2.7 interpreter? Or adjust the PATH in that context?

Thanks for reporting!

[Vynce]

Would an environment variable be sufficient?

Yeah, that could work. We could set that globally in our uv installation script (not that different from setting it in the uv.toml). We're already setting the default index url and python-install-mirror in the uv.toml.

Would it be feasible to specify the full path to your 2.7 interpreter? Or adjust the PATH in that context?

Not easily. We need to support a mixed environment where legacy scripts expect python to be Python 2.7. I really want ~/.local/bin to be first in the PATH since that's where all the uv goodies live, but a python.exe there will shadow others later in the PATH. Putting Python 2.7 before ~/.local/bin on the PATH could work, but introduces other complexities with managing PATH order. Dealing with all this nonsense with Python on Windows is why I'm so excited about uv 😄.

Also feel free to decide that uv isn't going to go out of its way to support coexistence with Python 2. That'll make me sad because --default is exactly the feature I want to use to manage Python 3 versions going forward, but I can create my own python3.exe symlink that points to the desired uv trampoline executable instead or come up with other workarounds 😊.

[zanieb]

Another question, is there a way you're invoking python.exe for Python 2 that would inform us that we should pass that invocation through to another executable?

I think some flag here is reasonable, just need to figure out how to express it.

[Vynce]

Python 2 is typically invoked via the shebang in the the Python script (e.g. #!/usr/bin/env python) in a Git Bash (aka msys bash) shell on Windows. We do it this way so it works the same on Linux and macOS. There are some shell scripts that explicitly call Python 2 scripts directly, like python myscript.py. Both cases assume that python is on the PATH and resolves to Python 2.