Broaden collections.Counter __iadd__, __isubtract__, __iand__, and __ior__ to accept any mapping (#10397)

Co-authored-by: Alex Waygood <[email protected]>

Author: qthequartermasterman

stdlib/collections/__init__.pyi

@@ -1,6 +1,6 @@
 import sys
 from _collections_abc import dict_items, dict_keys, dict_values
-from _typeshed import SupportsKeysAndGetItem, SupportsRichComparison, SupportsRichComparisonT
+from _typeshed import SupportsItems, SupportsKeysAndGetItem, SupportsRichComparison, SupportsRichComparisonT
 from typing import Any, Generic, NoReturn, TypeVar, overload
 from typing_extensions import Self, SupportsIndex, final
 
@@ -299,10 +299,10 @@ class Counter(dict[_T, int], Generic[_T]):
     def __pos__(self) -> Counter[_T]: ...
     def __neg__(self) -> Counter[_T]: ...
     # several type: ignores because __iadd__ is supposedly incompatible with __add__, etc.
-    def __iadd__(self, other: Counter[_T]) -> Self: ...  # type: ignore[misc]
-    def __isub__(self, other: Counter[_T]) -> Self: ...
-    def __iand__(self, other: Counter[_T]) -> Self: ...
-    def __ior__(self, other: Counter[_T]) -> Self: ...  # type: ignore[override,misc]
+    def __iadd__(self, other: SupportsItems[_T, int]) -> Self: ...  # type: ignore[misc]
+    def __isub__(self, other: SupportsItems[_T, int]) -> Self: ...
+    def __iand__(self, other: SupportsItems[_T, int]) -> Self: ...
+    def __ior__(self, other: SupportsItems[_T, int]) -> Self: ...  # type: ignore[override,misc]
     if sys.version_info >= (3, 10):
         def total(self) -> int: ...
         def __le__(self, other: Counter[Any]) -> bool: ...