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Add support for PEP 661 (sentinels) #21454

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Add support for PEP 661 (sentinels) #21454

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c641321
Add support for PEP 661 (sentinels)
JelleZijlstra May 10, 2026
4d00721
simplify
JelleZijlstra May 10, 2026
271a07c
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] May 10, 2026
190b7c5
test isinstance
JelleZijlstra May 10, 2026
cfa09f4
Fix sentinel cache restore
JelleZijlstra May 11, 2026
835bb3b
maybe fix
JelleZijlstra May 11, 2026
a2caece
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] May 11, 2026
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test isinstance
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@JelleZijlstra
JelleZijlstra committed May 10, 2026
commit 190b7c5d504e015e47f98f2d190ac99c0d9a102a
20 changes: 20 additions & 0 deletions test-data/unit/check-sentinels.test
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Original file line number Diff line number Diff line change
Expand Up @@ -85,3 +85,23 @@ def func(x: int | MISSING = MISSING) -> None:
assert_type(x, MISSING)

[builtins fixtures/sentinel.pyi]

[case testIsinstanceSentinel]
# flags: --python-version 3.15
from typing import assert_type
from typing_extensions import Sentinel

BUILTIN = sentinel("BUILTIN")
TYPEXT = Sentinel("TYPEXT")

def func(x: int | BUILTIN | TYPEXT) -> None:
if isinstance(x, sentinel):
assert_type(x, BUILTIN)
else:
assert_type(x, int | TYPEXT)
if isinstance(x, Sentinel):
assert_type(x, TYPEXT)
else:
assert_type(x, int)

[builtins fixtures/sentinel.pyi]
3 changes: 3 additions & 0 deletions test-data/unit/fixtures/sentinel.pyi
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Expand Up @@ -19,3 +19,6 @@ class sentinel:
def __init__(self, name: str, /) -> None: ...

class dict: pass
class tuple: pass

def isinstance(x: object, t: type) -> bool: pass
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