test_interpret fails: distlib.version.UnsupportedVersionError: Not a valid version: 3.13.0a1+

[hroncok]

Describe the bug

The tests of distlib fail with CPython built from git HEAD.

________________________ MarkersTestCase.test_interpret ________________________

self = <test_markers.MarkersTestCase testMethod=test_interpret>

    def test_interpret(self):
        sys_platform = sys.platform
        version = sys.version.split()[0]
        os_name = os.name
        platform_version = platform.version()
        platform_machine = platform.machine()
        platform_python_implementation = python_implementation()

        self.assertTrue(interpret("sys_platform == '%s'" % sys_platform))
>       self.assertTrue(interpret(
            "sys_platform == '%s' and python_full_version == '%s'" %
            (sys_platform, version)))

tests/test_markers.py:29: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
distlib/markers.py:153: in interpret
    return evaluator.evaluate(expr, context)
distlib/markers.py:83: in evaluate
    rhs = self.evaluate(erhs, context)
distlib/markers.py:86: in evaluate
    lhs = NV(lhs)
distlib/version.py:33: in __init__
    self._parts = parts = self.parse(s)
distlib/version.py:276: in parse
    result = _normalized_key(s)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

s = '3.13.0a1+'

    def _pep_440_key(s):
        s = s.strip()
        m = PEP440_VERSION_RE.match(s)
        if not m:
>           raise UnsupportedVersionError('Not a valid version: %s' % s)
E           distlib.version.UnsupportedVersionError: Not a valid version: 3.13.0a1+

distlib/version.py:188: UnsupportedVersionError

I don't believe that the Python version is supposed to follow PEP 440. Not sure if this is a problem in test, or in distlib itself.

To Reproduce Steps to reproduce the behavior:

1. Compile CPython from the main branch.
2. The version is 3.13.0a1+
3. Run tests of distlib
4. See UnsupportedVersionError

Expected behavior The tests should work with CPython built from git as well as CPython releases.

Screenshots No screenshot is neccessary.

Environment

• OS, including version: Fedora Linux 40
• Version of this library: 0.3.7 with e27569b02d9718c19ece71ce6d5124b967277399 applied on top

Additional information We (in Fedora) are testing various packages with pre-releases of Python. Normally we only use releases, but this time, we needed to fetch some reverts and built Python from git. This does not block us -- we will continue with 3.13.0a2 soon. But I thought this is worth reporting.

[vsajip]

I am away and won't be able to do any work on this myself before mid-December, but I will probably be able to review any submitted PRs before then.

[vsajip]

I can't reproduce this with 3.13.0a2+ with the repo version of distlib:

$ ~/projects/cpython/main/python --version
Python 3.13.0a2+
$ PYTHONHASHSEED=0 ~/projects/cpython/main/python tests/test_all.py
............................s.................................................s....s.......s........................s.ssssss..........sss...s..ss.........................s..........s..........................ssss.........ss.............
----------------------------------------------------------------------
Ran 215 tests in 26.665s

OK (skipped=25)