Local version labels in version specifiers

[edible-programs]

from packaging import requirements
requirements.parse_requirement("torch>=1.13.1+cu117")
# Expected end or semicolon (after version specifier)

[pradyunsg]

Argh, parse_requirement isn't supposed to be a public function.

Beyond that, >=1.13.1+cu117 isn't a valid version specifier per the existing language of PEP 508 and PEP 440. You can also see that this was being parsed as a LegacySpecifier within older versions of packaging (with 21.3 below).

>>> # packaging 21.3
>>> from packaging.requirements import Requirement
>>> list(Requirement("torch>=1.13.1+cu117").specifier)
[<LegacySpecifier('>=1.13.1+cu117')>]

It does have reasonable semantics if you expect to have a monotonically increasing number (although it'd work better with a . between cu and the number).

>>> # packaging 21.3
>>> Requirement("torch>=1.13.1+cu117").specifier.contains(Version("1.13.1+cu117"))
True
>>> Requirement("torch>=1.13.1+cu117").specifier.contains(Version("1.13.1+cu116"))
False
>>> Requirement("torch>=1.13.1+cu117").specifier.contains(Version("1.13.1+cu118"))
True

It does seem like a valid version specifier and a valid usecase but, as it stands, PEP 508 and PEP 440 don't permit using local version labels in version specifiers. This works in pip and packaging 21.3 for the same reasons that the following "works":

>>> # packaging 21.3
>>> list(Requirement("torch>=absolutelyanythinghere").specifier)
[<LegacySpecifier('>=absolutelyanythinghere')>]

[pradyunsg]

I've opened https://discuss.python.org/t/lets-permit-local-version-label-in-version-specifiers/22781 for discussing this.

[pradyunsg]

We’ve settled on no for this. See the discussion above for the details.