False negatives with `dict.(r)or` · Issue #10678 · python/typeshed · GitHub

I have code equivalent to the following:

from requests.structures import CaseInsensitiveDict

CaseInsensitiveDict() | dict()

mypy does not error.

My environment has:

mypy==1.5.1
types-requests==2.31.0.2
Python 3.11.5

At runtime I get:

TypeError: unsupported operand type(s) for |: 'CaseInsensitiveDict' and 'dict'

I would expect an [operator] error. For example, if I swap the CaseInsensitiveDict() for 1, I get:

error: Unsupported operand types for | ("int" and "dict[str, str]")  [operator]

I am happy to contribute, but I'm not sure what change is needed. I imagine a change is needed in https://github.com/python/typeshed/blob/main/stubs/requests/requests/structures.pyi.

In actual fact, the issue is our stubs for dict.__or__ and dict.__ror__:

typeshed/stdlib/builtins.pyi

Lines 1122 to 1129 in aa39b99

    
           @overload 
        
           def __or__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ... 
        
           @overload 
        
           def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ... 
        
           @overload 
        
           def __ror__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ... 
        
           @overload 
        
           def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...

We currently claim that dict.__(r)or__ accepts any Mapping, but this isn't actually true. At runtime, the object passed to dict.__or__ has to be an instance of dict (and requests.structures.CaseInsensitiveDict is not a subclass of dict).

Ideally we'd make this change, but I think we tried it recently, and it caused an unfortunate number of false positives:

diff --git a/stdlib/builtins.pyi b/stdlib/builtins.pyi
index 71cccee16..cf4f857c5 100644
--- a/stdlib/builtins.pyi
+++ b/stdlib/builtins.pyi
@@ -1120,13 +1120,13 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, __item: Any) -> GenericAlias: ...
         @overload
-        def __or__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
+        def __or__(self, __value: dict[_KT, _VT]) -> dict[_KT, _VT]: ...
         @overload
-        def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
+        def __or__(self, __value: dict[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
         @overload
-        def __ror__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
+        def __ror__(self, __value: dict[_KT, _VT]) -> dict[_KT, _VT]: ...
         @overload
-        def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
+        def __ror__(self, __value: dict[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
         # dict.__ior__ should be kept roughly in line with MutableMapping.update()
         @overload  # type: ignore[misc]
         def __ior__(self, __value: SupportsKeysAndGetItem[_KT, _VT]) -> Self: ...

Okay, making the type hints more accurate here is actually less disruptive than I thought it would be! See #10679 (comment)

Thank you for picking this up so quickly.

False negatives with `dict.(r)or` · Issue #10678 · python/typeshed · GitHub

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False negatives with dict.(r)or #10678

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	@overload
	def __or__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
	@overload
	def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT \| _T1, _VT \| _T2]: ...
	@overload
	def __ror__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...
	@overload
	def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT \| _T1, _VT \| _T2]: ...

False negatives with `dict.__(r)or__` · Issue #10678 · python/typeshed · GitHub

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False negatives with dict.__(r)or__ #10678

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AlexWaygood commented on Sep 7, 2023

AlexWaygood commented on Sep 7, 2023

adamtheturtle commented on Sep 7, 2023

sobolevn commented on Oct 11, 2023

AlexWaygood commented on Oct 12, 2023

AlexWaygood commented on Oct 12, 2023

sobolevn commented on Oct 18, 2023

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False negatives with `dict.(r)or` · Issue #10678 · python/typeshed · GitHub

False negatives with dict.(r)or #10678