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TypeAliasType can leak memory if name is a str subclass #140000
Description
Bug report
Bug description:
TypeAliasType's traverse implementation does not visit its name. This means that we can leak memory if name is passed an instance of a mutable str subclass.
from typing import TypeAliasType
import weakref
import gc
class S(str):
pass
def still_alive(ref):
obj = ref()
if not isinstance(obj, S):
return False
T = obj.T
if not isinstance(T, TypeAliasType):
return False
return T
name = S("name")
T = TypeAliasType(name, int)
name.T = T
ref = weakref.ref(name)
assert still_alive(ref)
del name
del T
gc.collect()
gc.collect()
assert still_alive(ref)
del ref().T
assert not still_alive(ref)CPython versions tested on:
CPython main branch
Operating systems tested on:
macOS
Linked PRs
- gh-140000: Traverse
nameattribute forTypeVar,TypeVarTuple,TypeAliasType,ParamSpec#140016 - [3.14] gh-140000: Traverse
nameattribute forTypeVar,TypeVarTuple,TypeAliasType,ParamSpec(GH-140016) #140063 - [3.13] gh-140000: Traverse
nameattribute forTypeVar,TypeVarTuple,TypeAliasType,ParamSpec(GH-140016) #140073
Activity
JelleZijlstra commentedon Oct 12, 2025
This also affects TypeVar, TypeVarTuple, and ParamSpec.
efimov-mikhail commentedon Oct 12, 2025
Leak for all 4 types is confirmed on main, 3.14 and 3.13 branches. PR with fix is submitted.
gh-140000: Traverse `name` attribute for `TypeVar`, `TypeVarTuple`, `…
pythongh-140000: Traverse `name` attribute for `TypeVar`, `TypeVarTup…
[3.14] gh-140000: Traverse `name` attribute for `TypeVar`, `TypeVarTu…
[3.13] gh-140000: Traverse `name` attribute for `TypeVar`, `TypeVarTu…