Recommend to use mypy error codes if applicable (#6305)

CONTRIBUTING.md

@@ -389,7 +389,9 @@ Some further tips for good type hints:
 * in Python 2, whenever possible, use `unicode` if that's the only
   possible type, and `Text` if it can be either `unicode` or `bytes`;
 * use platform checks like `if sys.platform == 'win32'` to denote
-  platform-dependent APIs.
+  platform-dependent APIs;
+* use mypy error codes for mypy-specific `# type: ignore` annotations,
+  e.g. `# type: ignore[override]` for Liskov Substitution Principle violations.
 
 Imports in stubs are considered private (not part of the exported API)
 unless:

stdlib/builtins.pyi

@@ -419,7 +419,7 @@ class str(Sequence[str]):
     def maketrans(__x: str, __y: str, __z: str | None = ...) -> dict[int, int | None]: ...
     def __add__(self, __s: str) -> str: ...
     # Incompatible with Sequence.__contains__
-    def __contains__(self, __o: str) -> bool: ...  # type: ignore
+    def __contains__(self, __o: str) -> bool: ...  # type: ignore[override]
     def __eq__(self, __x: object) -> bool: ...
     def __ge__(self, __x: str) -> bool: ...
     def __getitem__(self, __i: int | slice) -> str: ...
@@ -528,7 +528,7 @@ class bytes(ByteString):
     def __rmul__(self, __n: SupportsIndex) -> bytes: ...
     def __mod__(self, __value: Any) -> bytes: ...
     # Incompatible with Sequence.__contains__
-    def __contains__(self, __o: SupportsIndex | bytes) -> bool: ...  # type: ignore
+    def __contains__(self, __o: SupportsIndex | bytes) -> bool: ...  # type: ignore[override]
     def __eq__(self, __x: object) -> bool: ...
     def __ne__(self, __x: object) -> bool: ...
     def __lt__(self, __x: bytes) -> bool: ...
@@ -620,7 +620,7 @@ class bytearray(MutableSequence[int], ByteString):
     def __iter__(self) -> Iterator[int]: ...
     def __str__(self) -> str: ...
     def __repr__(self) -> str: ...
-    __hash__: None  # type: ignore
+    __hash__: None  # type: ignore[assignment]
     @overload
     def __getitem__(self, __i: SupportsIndex) -> int: ...
     @overload
@@ -637,7 +637,7 @@ class bytearray(MutableSequence[int], ByteString):
     def __imul__(self, __n: SupportsIndex) -> bytearray: ...
     def __mod__(self, __value: Any) -> bytes: ...
     # Incompatible with Sequence.__contains__
-    def __contains__(self, __o: SupportsIndex | bytes) -> bool: ...  # type: ignore
+    def __contains__(self, __o: SupportsIndex | bytes) -> bool: ...  # type: ignore[override]
     def __eq__(self, __x: object) -> bool: ...
     def __ne__(self, __x: object) -> bool: ...
     def __lt__(self, __x: bytes) -> bool: ...
@@ -728,7 +728,7 @@ class slice(object):
     def __init__(self, __stop: Any) -> None: ...
     @overload
     def __init__(self, __start: Any, __stop: Any, __step: Any = ...) -> None: ...
-    __hash__: None  # type: ignore
+    __hash__: None  # type: ignore[assignment]
     def indices(self, __len: SupportsIndex) -> tuple[int, int, int]: ...
 
 class tuple(Sequence[_T_co], Generic[_T_co]):
@@ -785,7 +785,7 @@ class list(MutableSequence[_T], Generic[_T]):
     def __len__(self) -> int: ...
     def __iter__(self) -> Iterator[_T]: ...
     def __str__(self) -> str: ...
-    __hash__: None  # type: ignore
+    __hash__: None  # type: ignore[assignment]
     @overload
     def __getitem__(self, __i: SupportsIndex) -> _T: ...
     @overload
@@ -850,12 +850,12 @@ class dict(MutableMapping[_KT, _VT], Generic[_KT, _VT]):
     if sys.version_info >= (3, 8):
         def __reversed__(self) -> Iterator[_KT]: ...
     def __str__(self) -> str: ...
-    __hash__: None  # type: ignore
+    __hash__: None  # type: ignore[assignment]
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, __item: Any) -> GenericAlias: ...
         def __or__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
         def __ror__(self, __value: Mapping[_T1, _T2]) -> dict[_KT | _T1, _VT | _T2]: ...
-        def __ior__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...  # type: ignore
+        def __ior__(self, __value: Mapping[_KT, _VT]) -> dict[_KT, _VT]: ...  # type: ignore[misc]
 
 class set(MutableSet[_T], Generic[_T]):
     def __init__(self, __iterable: Iterable[_T] = ...) -> None: ...
@@ -892,7 +892,7 @@ class set(MutableSet[_T], Generic[_T]):
     def __lt__(self, __s: AbstractSet[object]) -> bool: ...
     def __ge__(self, __s: AbstractSet[object]) -> bool: ...
     def __gt__(self, __s: AbstractSet[object]) -> bool: ...
-    __hash__: None  # type: ignore
+    __hash__: None  # type: ignore[assignment]
     if sys.version_info >= (3, 9):
         def __class_getitem__(cls, __item: Any) -> GenericAlias: ...
 
@@ -938,7 +938,7 @@ class range(Sequence[int]):
     @overload
     def __init__(self, __start: SupportsIndex, __stop: SupportsIndex, __step: SupportsIndex = ...) -> None: ...
     def count(self, __value: int) -> int: ...
-    def index(self, __value: int) -> int: ...  # type: ignore
+    def index(self, __value: int) -> int: ...  # type: ignore[override]
     def __len__(self) -> int: ...
     def __contains__(self, __o: object) -> bool: ...
     def __iter__(self) -> Iterator[int]: ...
@@ -968,10 +968,10 @@ class property(object):
     def __delete__(self, __obj: Any) -> None: ...
 
 @final
-class _NotImplementedType(Any):  # type: ignore
+class _NotImplementedType(Any):  # type: ignore[misc]
     # A little weird, but typing the __call__ as NotImplemented makes the error message
     # for NotImplemented() much better
-    __call__: NotImplemented  # type: ignore
+    __call__: NotImplemented  # type: ignore[valid-type]
 
 NotImplemented: _NotImplementedType
 

tests/mypy_test.py

@@ -207,6 +207,7 @@ def get_mypy_flags(args, major: int, minor: int, temp_name: str, *, custom_types
             "--no-implicit-optional",
             "--disallow-any-generics",
             "--warn-incomplete-stub",
+            "--show-error-codes",
             "--no-error-summary",
         ]
     if custom_typeshed: