uv fails to find python in non-venv install on Windows

[gaborbernat]

When trying to run the tool on Windows, I get this rust like stack trace:

Error: The system cannot find the file specified.
 (from CreateProcessA(null(), child_cmdline.into_bytes_with_nul().as_mut_ptr(),
    null(), null(), 1, 0, null(), null(), addr_of!(*si),
    child_process_info.as_mut_ptr()))

See https://github.com/tox-dev/tox-uv/actions/runs/7978647392/job/21784221224?pr=19

I'm using uv find_uv_bin...

[AlexWaygood]

Interesting, this is the same error I was getting in #1639 (cc. @MichaReiser)

[AlexWaygood]

Have you created and activated a virtual environment? My and Micha's conclusion from debugging #1639 was that it's not possible on Windows (yet) to use the "trick" where you pretend a virtual environment has been created and activated by doing the echo "VIRTUAL_ENV=${Python_ROOT_DIR}" >> $GITHUB_ENV in a GitHub Actions workflow. The reason why this doesn't work on Windows is likely due to the fact that python.exe is found in a different directory on Windows when a virtual environment hasn't been activated (it's not in a Scripts/ directory when a virtual environment hasn't been activated, and uv assumes python.exe will always be in a Scripts/ directory on Windows). So the VIRTUAL_ENV trick to avoid having to create and activate an environment currently only works on Unix.

(Edit: it looks like you are indeed doing the Unix-only "trick": https://github.com/tox-dev/tox-uv/blob/a93e37e98a012d07d6ac151e097c444a77d15b0a/.github/workflows/check.yml#L43)

[AlexWaygood]

I outlined a cross-platform way of using uv in a GitHub Actions workflow here: https://github.com/astral-sh/uv/issues/1386#issuecomment-1952420541

[gaborbernat]

Yeah, I can do that, but sounds more like a workaround than a solution for the underlying problem 👍

[AlexWaygood]

Yeah, I can do that, but sounds more like a workaround than a solution for the underlying problem 👍

Oh of course. Longer-term we want to have first-class support for GitHub Actions, which I think will probably include something like #1526. We absolutely agree the current situation is far from ideal :)

[jenshnielsen]

I ran into this error when trying to run pytest installed with uv from a pre existing conda environment.

[MichaReiser]

The main issue here is that uv assumes that Python is located at $VIRTUAL_ENV/Scripts/python.exe which isn't the case when pointing to a global python installation. see https://github.com/astral-sh/uv/pull/1803 for some details.

@jenshnielsen https://github.com/astral-sh/uv/pull/1803 might help with your issue, depending on the layout of the venv directory

[Pixel-Minions]

I wonder of this is related to the same issue I am having with embedded versions of Python: https://github.com/astral-sh/uv/issues/1656

[mkleinbort]

Is a solution for this in the works? I'm preparing an internal talk on UV for users that use windows and keen to know what they should expect.

[MichaReiser]

We're planning to solve this as part of https://github.com/astral-sh/uv/issues/1526

The recommended local workflow is to use a venv instead of installing dependencies globally.

[charliermarsh]

Yup I'm on it.