Make the frozen dataclasses picklable

[nraynaud]

What's the problem this feature will solve?

it's probably nice to let people pickle the result of a requirements.txt parsing
here is a dependent that broke (indirectly pickling ParsedRequirement):

achillesrasquinha/pipupgrade#161

Describe the solution you'd like

I'm not even sure it's the right place to ask this, just submitting an idea.

The technical solutions are discussed on SO:
https://stackoverflow.com/a/69556666

Alternative Solutions

None

Additional context

https://github.com/achillesrasquinha/pipupgrade

Code of Conduct

• I agree to follow the PSF Code of Conduct.

[notatallshaw]

It seems like this can be fixed once Python 3.9 support is dropped by adding slots=True: python/cpython#80605

[notatallshaw]

I'm not sure what appetite there is for this, but in the mean time the dataclass definitions could be different for Python 3.10+ vs. Python 3.9.

[ichard26]

I'd much rather revert the dataclass commit for this class then maintain two definitions of the same class, although looking at the larger picture, pip does not have a public API. This is intentional because we don't want to be in the business of maintaining one and dealing with the codebase restrictions that come with it. I know that we've historically accommodated pip-tools, but a part of the unique relationship is that there is (was? not sure anymore) some overlap in maintainers between the two projects.

FWIW, it looks like pipupgrade is in maintenance-only mode or unmaintained: achillesrasquinha/pipupgrade#158.

For the time being, you can look into uv which may have something similar to pipupgrade.

[notatallshaw]

although looking at the larger picture, pip does not have a public API

Agreed, a PR to "fix" this issue would need to stand on its own merits, separate from pipupgrade.

For the time being, you can look into uv which may have something similar to pipupgrade.

Reading pipupgrades description page, other than being a package manager in some sense, there doesn't appear to be much overlap of the UX between uv and pipupgrade. So other project and environment managers such as PDM, hatch, poetry, pixi, and pip-tools should be mentioned as also a way of managing what packages you have and being able to upgrade them consistently.

[nraynaud]

pip does not have a public API. This is intentional because we don't want to be in the business of maintaining one and dealing with the codebase restrictions that come with it.

I was more or less expecting that, I just didn't want to assume.

[notatallshaw]

I'm going to add this to the pip 26.1 milestone, on the assumption that's when pip drops Python 3.9 support to remind us to use slots=True on our dataclasses:

pip/src/pip/_internal/req/req_file.py

Lines 105 to 109 in a0dead9

	@dataclass(frozen=True)
	class ParsedRequirement:
	# TODO: replace this with slots=True when dropping Python 3.9 support.
	__slots__ = (
	"requirement",

[pradyunsg]

@notatallshaw Could you file a smaller scoped issue for that and track the slots change with that?

I'm wary about the risks of conflating the change we want to make for our internals with this request for an unsupported-API usage pattern.