Pixi updates python without being asked

[liquidcarbon]

Checks

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pixi, using pixi --version.

Reproducible example

From empty folder with minimal pyproject.toml
Windows shown here, same on Linux.

[project]
name = "test"
description = "Minimal pyproject.toml with minimal [tool.pixi] section."

[tool.pixi.project]
channels = ["conda-forge"]
platforms = ["win-64"]

PS C:\Users\a\py> pixi add python=3.11
✔ Added python=3.11
PS C:\Users\a\py> pixi run python -VV
Python 3.11.8 | packaged by conda-forge | (main, Feb 16 2024, 20:40:50) [MSC v.1937 64 bit (AMD64)]


PS C:\Users\a\py> pixi add numpy
✔ Added numpy
PS C:\Users\a\py> pixi run python -VV
Python 3.12.2 | packaged by conda-forge | (main, Feb 16 2024, 20:42:31) [MSC v.1937 64 bit (AMD64)]

Final pyproject.toml becomes:

[project]
name = "test"
description = "Minimal pyproject.toml with minimal [tool.pixi] section."

[tool.pixi.project]
channels = ["conda-forge"]
platforms = ["win-64"]

[tool.pixi.dependencies]
python = "3.11.*"
numpy = ">=1.26.4,<1.27"

Issue description

Pixi updates python to latest without being asked to do so

Expected behavior

Keep python what it was

[tdejager]

Yes, I can definitely reproduce, even with the following toml:

[project]
name = "test"
description = "Minimal pyproject.toml with minimal [tool.pixi] section."

[tool.pixi.project]
channels = ["conda-forge"]
platforms = ["osx-arm64"]

[tool.pixi.dependencies]
python = ">=3.11,<3.12"
numpy = ">=1.26.4,<1.27"

and just running pixi install I get a 3.12 version.

Adding a requires-python = "<3.12", seems to constrain python again. I haven't investigated but, I think it's adding a default when the requires-python is missing that overwrites the explicit dependency. @olivier-lacroix might be interesting for you as well :)

[liquidcarbon]

with requires-python I had different troubles:

these
==3.11
==3.11.*
~=3.11
not sure but possibly ">=3.11,<3.12" as well

all gave me 3.11.0 instead of 3.11.8

[olivier-lacroix]

Hum. Currently, if there is no requires_python, a conda python dependency is added to the manifest (without any version specifier). My hypothesis was that the solver would provide the version that matched all predicates: is that incorrect?

[liquidcarbon]

It would probably make sense in the absence of "requires-python" to fall back to what's in tool.pixi ?

[olivier-lacroix]

Definitely. The intent was to take both into account, letting the solver do the hard job

[wolfv]

I started on some improvements in #1201 - would be happy to hear your opinions :)