Fix false negative dangerous-default-value for typing.NamedTuple (#3716)#10989
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hamza-mobeen wants to merge 2 commits intopylint-dev:mainfrom
Open
Fix false negative dangerous-default-value for typing.NamedTuple (#3716)#10989hamza-mobeen wants to merge 2 commits intopylint-dev:mainfrom
hamza-mobeen wants to merge 2 commits intopylint-dev:mainfrom
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DanielNoord
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May 3, 2026
| self.linter.stats.node_count["module"] += 1 | ||
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| def visit_classdef(self, _: nodes.ClassDef) -> None: | ||
| @utils.only_required_for_messages("dangerous-default-value") |
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This feels incorrect, considering we're also updating statistics here.
| continue | ||
| default = child.value | ||
| try: | ||
| value = next(default.infer()) |
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Should we use safe_infer here?
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Type of Changes
Description
Right now, pylint's
dangerous-default-value(W0102) only catches mutable defaults on regular function and method arguments. But the exact same bug can happen withtyping.NamedTuplefield defaults and pylint stays silent about it.Root cause
The existing
_check_dangerous_defaultmethod is only triggered viavisit_functiondef, which inspectsnode.args.defaults. When a class inherits fromtyping.NamedTuple, the field defaults areAnnAssignnodes inside aClassDefbody — the checker never sees them.What this PR does
Adds a new
_check_namedtuple_dangerous_defaultsmethod toBasicCheckerthat:typing.NamedTuple(using the sameancestor.qname()pattern already used invariables.pyanddesign_analysis.py)AnnAssignnodes in the class bodyDEFAULT_ARGUMENT_SYMBOLSmapdangerous-default-valueon the specific field lineThe check is called from
visit_classdef, which was updated with the@utils.only_required_for_messages("dangerous-default-value")decorator.Code change
In
pylint/checkers/base/basic_checker.py:The new
_check_namedtuple_dangerous_defaultsmethod reuses the same mutable-default detection logic from_check_dangerous_default, applied toAnnAssign.valuenodes instead of function argument defaults.Tests
Added a new functional test
dangerous_default_value_namedtuple.pycovering:[],{},set(),{1, 2}(set literal),list(),dict(),collections.deque()defaults → all emit W0102str,int,bool,tuple,frozenset) → no warningCloses #3716
Checklist
skip-newsif the change does not need to be in the changelog.towncrier create <IssueNumber>.<type>which will beincluded in the changelog.
<type>can be one of the types defined in./towncrier.toml.If necessary you can write details or offer examples on how the new change is supposed to work.
tox -e docsDon't hesitate to open multiple PRs if the change requires it. If your review is so
big it requires to actually plan and allocate time to review, it's more likely
that it's going to go stale.
and preferred name in
script/.contributors_aliases.json