Allow dependency groups to define a separate `requires-python`

[zanieb]

Summary

Right now, the [dependency-groups] have the same requires-python as the [project] defines, but this causes problems when a group is only intended to be used with a different Python version range, e.g., you could only care about 3.12+ for building your documentation but 3.9+ matters for publishing your library.

See

• Mininum Python requirement from dependency greater than root project. #11605

As a meta-note, I know this was discussed elsewhere but cannot find it.

Example

[project]
name = "example"
version = "0.0.0"
requires-python = ">=3.10"

[tool.uv.dependency-groups.foo]
requires-python = ">=3.12"

[konstin]

To add a motivating example, users may have tooling such as building documentation, code generation or importing external data that requires a more recent Python version than the project itself. A common example is sphinx, which (as of master) requires Python 3.11, while libraries supporting all non-EOL Python versions support >=3.9. The current workaround is sphinx; python_version >= "3.11" in the dependency group, which allows selecting the group on an older Python version without actually installing sphinx.

[charliermarsh]

I think this is fairly straightforward to implement by adding it to lowering.rs (just put python_version >= "3.12" on each dependency; the resolver will do the rest). However, we probably also want to error (?) if users try to install these groups with a lower Python version? So we'll need to track it elsewhere too, and add error handling around it.

[zanieb]

I see this as fairly high priority given the workaround is to add a marker to every dependency in the group.

@Gankra perhaps you'd be interested in picking it up? (I know you love dependency groups)

[charliermarsh]

(The only weirdness with the approach I described above is we'll then add python_version >= "3.12" to each of the dependency entries in the lockfile and we'd have some annotation on the group itself, which is kind of ugly.)

[Gankra]

Sure I can give this a shot

[a-reich]

I’d love this feature too, it’s analogous to one hatch has (for what it terms environments).

[RobertCraigie]

We're running into this as well, as all of our libraries still support Python 3.8, we can't add an optional dependency that requires 3.9. From our perspective it's totally fine if users can only use some optional dependencies if they're on later Python versions.

Is there any workaround possible until this is fully supported?