Fix frozendict constructor: drop the argument-less __init__ (#15985)#15989
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hauntsaninja merged 2 commits intoJul 8, 2026
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frozendict has __new__ overloads for keyword arguments, a mapping and an iterable of pairs, but also declared 'def __init__(self) -> None: ...', so type checkers rejected 'frozendict(a=1)' etc. with 'Expected 0 positional arguments'. Remove the redundant __init__ (like other __new__-constructed builtins) so the __new__ overloads govern construction. Added a test case.
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hauntsaninja
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Jul 8, 2026
| from typing import Any | ||
| from typing_extensions import assert_type | ||
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| # Regression test for gh-15985: ``frozendict`` can be constructed from keyword |
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might need an if sys.version_info >= (3, 15): top level block
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Good catch — done. Wrapped the assertions in an if sys.version_info >= (3, 15): block (matching check_exception_group-py311.py), so the file also type-checks cleanly on earlier target versions instead of tripping on the undefined frozendict name.
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According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉 |
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Fixes #15985.
The new (3.15)
frozendictbuiltin has__new__overloads for keyword arguments, a mapping, and an iterable of pairs, but the stub also declared:Because type checkers validate a constructor call against both
__new__and__init__, that argument-less__init__madefrozendict(a=1),frozendict({...}), andfrozendict([...])all fail with "Expected 0 positional arguments" / "Too many arguments".Removing the redundant
__init__lets the__new__overloads govern construction (matching other__new__-constructed builtins liketuple/frozenset, which don't declare a restrictive__init__).Added
check_frozendict-py315.pycovering the keyword / mapping / iterable / mixed forms; it fails onmainand passes with this change.tests/mypy_test.py stdlib/builtins.pyisucceeds.Disclosure: prepared with AI assistance; reviewed and verified locally.