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Remove PEP-604 methods from Sentinel on Python <3.10 #605

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Merged
merged 3 commits into from
May 25, 2025
Merged

Remove PEP-604 methods from Sentinel on Python <3.10 #605

merged 3 commits into from
May 25, 2025

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AlexWaygood
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We don't generally try to "backport PEP 604" on Python <3.10; this is more consistent with our features

@AlexWaygood
Remove PEP-604 methods from Sentinel on Python <3.10
c9fba13 
We don't generally try to "backport PEP 604" on Python <3.10; this is more consistent with our features
AlexWaygood
AlexWaygood commented May 25, 2025
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@AlexWaygood AlexWaygood mentioned this pull request May 25, 2025
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@JelleZijlstra
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Could you add a note to the changelog?

@AlexWaygood AlexWaygood requested a review from JelleZijlstra May 25, 2025 15:34
@JelleZijlstra
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Note that typing_extensions._SpecialForm also unconditionally has __or__.

$ uv run python3.9
Python 3.9.0rc1 (v3.9.0rc1:439c93d51f, Aug 11 2020, 16:45:30) 
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing_extensions import Self, LiteralString
>>> Self | LiteralString
typing.Union[typing_extensions.Self, typing_extensions.LiteralString]
>>>

Probably not worth fixing at this point though.

@JelleZijlstra
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It's suspicious that no tests failed, would you mind adding a simple 3.10+ test that __or__ works?

@AlexWaygood
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Note that typing_extensions._SpecialForm also unconditionally has __or__.

Yes, the word "generally" in the changelog entry is doing some work here 😄 as you say, though, _SpecialForm.__(r)or__ is probably not doing much harm, and it might cause backwards-compat issues to remove it now 🤷

@AlexWaygood
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It's suspicious that no tests failed, would you mind adding a simple 3.10+ test that __or__ works?

it actually is already tested on Python 3.10+, but the test is already skipped on Python <=3.9!

typing_extensions/src/test_typing_extensions.py

Lines 9148 to 9156 in 44de568

@skipIf(sys.version_info < (3, 10), reason='New unions not available in 3.9')
def test_sentinel_type_expression_union(self):
sentinel = Sentinel('sentinel')
def func1(a: int | sentinel = sentinel): pass
def func2(a: sentinel | int = sentinel): pass
self.assertEqual(func1.__annotations__['a'], Union[int, sentinel])
self.assertEqual(func2.__annotations__['a'], Union[sentinel, int])

@JelleZijlstra JelleZijlstra merged commit fadc1ed into main May 25, 2025
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@JelleZijlstra JelleZijlstra deleted the AlexWaygood-patch-1 branch May 25, 2025 15:42
@Viicos
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Viicos commented May 25, 2025

Thanks @AlexWaygood, now that this is version guarded we could in fact return operator.or_(self, other), so that in typeshed we expose -> UnionType in >=3.10 instead of >=3.14.

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AlexWaygood commented May 25, 2025 •
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@Viicos I don't think that works, does it? operator.or_ just calls __or__, so we can't call operator.or_ from __or__ without infinite recursion:

~/dev/typing_extensions/src (main)⚡ % git diff          
diff --git a/src/typing_extensions.py b/src/typing_extensions.py
index 292641a..73caf8d 100644
--- a/src/typing_extensions.py
+++ b/src/typing_extensions.py
@@ -4246,10 +4246,10 @@ class Sentinel:
 
     if sys.version_info >= (3, 10):
         def __or__(self, other):
-            return typing.Union[self, other]
+            return operator.or_(self, other)
 
         def __ror__(self, other):
-            return typing.Union[other, self]
+            return operator.or_(self, other)
 
     def __getstate__(self):
         raise TypeError(f"Cannot pickle {type(self).__name__!r} object")
~/dev/typing_extensions/src (main)⚡ % python                   
Python 3.13.1 (main, Jan  3 2025, 12:04:03) [Clang 15.0.0 (clang-1500.3.9.4)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from typing_extensions import TypeVar, Sentinel
>>> Sentinel("T") | Sentinel("T")
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    Sentinel("T") | Sentinel("T")
    ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~
  File "/Users/alexw/dev/typing_extensions/src/typing_extensions.py", line 4249, in __or__
    return operator.or_(self, other)
           ~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/Users/alexw/dev/typing_extensions/src/typing_extensions.py", line 4249, in __or__
    return operator.or_(self, other)
           ~~~~~~~~~~~~^^^^^^^^^^^^^
  File "/Users/alexw/dev/typing_extensions/src/typing_extensions.py", line 4249, in __or__
    return operator.or_(self, other)
           ~~~~~~~~~~~~^^^^^^^^^^^^^
  [Previous line repeated 988 more times]
RecursionError: maximum recursion depth exceeded
>>>

UnionType also doesn't support wrapping objects that aren't instances of type on Python <3.14

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Viicos commented May 25, 2025

Good catch, I always fall into this recursion trap!

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@AlexWaygood @JelleZijlstra @Viicos