Request for changing python versions more easily

[brenorb]

I just started trying uv, so I started

uv init
uv add pandas
...
uv add transformers

Then I got an error. The project initialized using python 3.13 and transformers couldn't support that ( error: the configured Python interpreter version (3.13) is newer than PyO3's maximum supported version (3.12)). So I tried to no avail:

uv python install 3.9
uv python uninstall 3.13
uv python pin 3.9
uv venv --python 3.9

I also manually changed .python-version from 3.13 to 3.9, but it didn't work as well. I was always getting the same error:

error: The requested Python version `3.9` is incompatible with the project `requires-python` value of `>=3.13`.

Now I know that I can use uv init --python 3.9, but then I would need to erase everything and start again. I know I could also use uv run --python 3.9 example.py but I don't write this all the time.

I eventually could solve the issue manually changing pyproject.toml from requires-python = ">=3.13" to requires-python = ">=3.9", but it could be done in the command line. I'm suggesting to add a command to change the requires-python value without needing to manually rewrite the file, and maybe having some link between .python-version and the pyproject.toml.

If there is a better way, I'd love to know about it.

I'm using uv 0.4.25 (Homebrew 2024-10-21)

[zanieb]

Sorry you ran into problems here. I'm not sure what our best option is for changing requires-python. It doesn't quite seem worth a dedicated command.

[inikolaev]

That would be really great to have support out-of-the-box. It's often a painful process with many package managers such as pipenv and poetry and worse it's not usually very well documented.

What I often want is to migrate my application from one Python version to another and minimise the amount of packages I have to upgrade to the minimum. But most package managers eagerly upgrade all dependencies if you approach this in a naive way. With pipenv what I happen to do is update Python version in Pipfile and then "upgrade" some package to trick pipenv to regenerate the lock file.

[ChrisAichinger]

I ran into the same issue: new to uv, needed to change Python version due to some incompatible libraries.

My main issue was the the solution was not discoverable: I didn't find any documentation about how to upgrade the Python version in an existing project. I was happy to finally stumble across this Github issue.

My solution:

rm -rf .python-version .venv
mv pyproject.toml pyproject.old
uv init --python 3.11
uv add ...  // add all libraries from pyproject.old

So maybe uv doesn't need a separate command for it, but better documentation would be fantastic.

[brenorb]

Or maybe just link .python-version file somehow with requires-python value inside pyproject.toml.