Add support for dict.{keys,values,items}.mapping (#6039)

Co-authored-by: KotlinIsland <kotlinisland@users.noreply.github.com>

stdlib/builtins.pyi

@@ -21,7 +21,7 @@ from _typeshed import (
 )
 from ast import AST, mod
 from io import BufferedRandom, BufferedReader, BufferedWriter, FileIO, TextIOWrapper
-from types import CodeType, TracebackType
+from types import CodeType, MappingProxyType, TracebackType
 from typing import (
     IO,
     AbstractSet,
@@ -73,6 +73,8 @@ _T_co = TypeVar("_T_co", covariant=True)
 _T_contra = TypeVar("_T_contra", contravariant=True)
 _KT = TypeVar("_KT")
 _VT = TypeVar("_VT")
+_KT_co = TypeVar("_KT_co", covariant=True)  # Key type covariant containers.
+_VT_co = TypeVar("_VT_co", covariant=True)  # Value type covariant containers.
 _S = TypeVar("_S")
 _T1 = TypeVar("_T1")
 _T2 = TypeVar("_T2")
@@ -787,6 +789,20 @@ class list(MutableSequence[_T], Generic[_T]):
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, item: Any) -> GenericAlias: ...
 
+class _dict_keys(KeysView[_KT_co], Generic[_KT_co, _VT_co]):
+    if sys.version_info >= (3, 10):
+        mapping: MappingProxyType[_KT_co, _VT_co]
+
+# The generics are the wrong way around because of a mypy limitation
+#  https://github.com/python/mypy/issues/11138
+class _dict_values(ValuesView[_VT_co], Generic[_VT_co, _KT_co]):
+    if sys.version_info >= (3, 10):
+        mapping: MappingProxyType[_KT_co, _VT_co]
+
+class _dict_items(ItemsView[_KT_co, _VT_co], Generic[_KT_co, _VT_co]):
+    if sys.version_info >= (3, 10):
+        mapping: MappingProxyType[_KT_co, _VT_co]
+
 class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     @overload
     def __init__(self: dict[_KT, _VT]) -> None: ...
@@ -807,9 +823,9 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     def update(self, __m: Iterable[Tuple[_KT, _VT]], **kwargs: _VT) -> None: ...
     @overload
     def update(self, **kwargs: _VT) -> None: ...
-    def keys(self) -> KeysView[_KT]: ...
-    def values(self) -> ValuesView[_VT]: ...
-    def items(self) -> ItemsView[_KT, _VT]: ...
+    def keys(self) -> _dict_keys[_KT, _VT]: ...
+    def values(self) -> _dict_values[_VT, _KT]: ...
+    def items(self) -> _dict_items[_KT, _VT]: ...
     @classmethod
     @overload
     def fromkeys(cls, __iterable: Iterable[_T], __value: None = ...) -> dict[_T, Any | None]: ...

stdlib/collections/__init__.pyi

@@ -1,28 +1,19 @@
 import sys
 from _typeshed import Self
+from builtins import _dict_items, _dict_keys, _dict_values
 from typing import Any, Dict, Generic, NoReturn, Tuple, Type, TypeVar, overload
 
 if sys.version_info >= (3, 10):
-    from typing import (
-        Callable,
-        ItemsView,
-        Iterable,
-        Iterator,
-        KeysView,
-        Mapping,
-        MutableMapping,
-        MutableSequence,
-        Reversible,
-        Sequence,
-        ValuesView,
-    )
+    from typing import Callable, Iterable, Iterator, Mapping, MutableMapping, MutableSequence, Reversible, Sequence
 else:
     from _collections_abc import *
 
 _S = TypeVar("_S")
 _T = TypeVar("_T")
 _KT = TypeVar("_KT")
 _VT = TypeVar("_VT")
+_KT_co = TypeVar("_KT_co", covariant=True)
+_VT_co = TypeVar("_VT_co", covariant=True)
 
 # namedtuple is special-cased in the type checker; the initializer is ignored.
 if sys.version_info >= (3, 7):
@@ -247,23 +238,25 @@ class Counter(Dict[_T, int], Generic[_T]):
     def __iand__(self, other: Counter[_T]) -> Counter[_T]: ...
     def __ior__(self, other: Counter[_T]) -> Counter[_T]: ...  # type: ignore
 
-class _OrderedDictKeysView(KeysView[_KT], Reversible[_KT]):
-    def __reversed__(self) -> Iterator[_KT]: ...
+class _OrderedDictKeysView(_dict_keys[_KT_co, _VT_co], Reversible[_KT_co]):
+    def __reversed__(self) -> Iterator[_KT_co]: ...
 
-class _OrderedDictItemsView(ItemsView[_KT, _VT], Reversible[Tuple[_KT, _VT]]):
-    def __reversed__(self) -> Iterator[Tuple[_KT, _VT]]: ...
+class _OrderedDictItemsView(_dict_items[_KT_co, _VT_co], Reversible[Tuple[_KT_co, _VT_co]]):
+    def __reversed__(self) -> Iterator[Tuple[_KT_co, _VT_co]]: ...
 
-class _OrderedDictValuesView(ValuesView[_VT], Reversible[_VT]):
-    def __reversed__(self) -> Iterator[_VT]: ...
+# The generics are the wrong way around because of a mypy limitation
+#  https://github.com/python/mypy/issues/11138
+class _OrderedDictValuesView(_dict_values[_VT_co, _KT_co], Reversible[_VT_co], Generic[_VT_co, _KT_co]):
+    def __reversed__(self) -> Iterator[_VT_co]: ...
 
 class OrderedDict(Dict[_KT, _VT], Reversible[_KT], Generic[_KT, _VT]):
     def popitem(self, last: bool = ...) -> Tuple[_KT, _VT]: ...
     def move_to_end(self, key: _KT, last: bool = ...) -> None: ...
     def copy(self: _S) -> _S: ...
     def __reversed__(self) -> Iterator[_KT]: ...
-    def keys(self) -> _OrderedDictKeysView[_KT]: ...
+    def keys(self) -> _OrderedDictKeysView[_KT, _VT]: ...
     def items(self) -> _OrderedDictItemsView[_KT, _VT]: ...
-    def values(self) -> _OrderedDictValuesView[_VT]: ...
+    def values(self) -> _OrderedDictValuesView[_VT, _KT]: ...
 
 class defaultdict(Dict[_KT, _VT], Generic[_KT, _VT]):
     default_factory: Callable[[], _VT] | None