Implement PEP 800 (@disjoint_base)#19678
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JukkaL merged 6 commits intopython:masterfrom Aug 19, 2025
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https://peps.python.org/pep-0800/ - Recognize the @disjoint_base decorator - Error if a class definition has incompatible disjoint bases - Recognize that classes with incompatible disjoint bases cannot exist - Check in stubtest that @disjoint_base is correctly applied
JelleZijlstra
commented
Aug 18, 2025
| return analyze_var(name, defn.var, itype, mx) | ||
| typ = function_type(defn, mx.chk.named_type("builtins.function")) | ||
| is_trivial_self = False | ||
| if isinstance(defn, Decorator): |
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This condition can never match because we already check for Decorator a few lines up.
for more information, see https://pre-commit.ci
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Primer analysis:
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JukkaL
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Aug 19, 2025
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JukkaL
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JukkaL
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Thanks for implementing the feature! Looks good, just a few ideas about additional things to test.
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| class C1: pass | ||
| class C2(Disjoint1, C1): pass | ||
| class C3(DisjointChild, Disjoint1): pass |
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Some ideas for additional test cases:
- Test reversed order of bases.
- Test with all three
Disjoint*bases. - Test a subclass of
C3/C2.
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Done, also added some more tests.
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Diff from mypy_primer, showing the effect of this PR on open source code: mypy (https://github.com/python/mypy)
+ mypy/checkmember.py:1488: error: Subclass of "FuncBase" and "Decorator" cannot exist: have distinct disjoint bases [unreachable]
+ mypy/checkmember.py:1488: note: See https://mypy.rtfd.io/en/stable/_refs.html#code-unreachable for more info
+ mypy/checkmember.py:1490: error: Statement is unreachable [unreachable]
steam.py (https://github.com/Gobot1234/steam.py)
- steam/chat.py:161: error: Unused "type: ignore" comment [unused-ignore]
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JukkaL
approved these changes
Aug 19, 2025
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https://peps.python.org/pep-0800/
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