From 4fdc78a7b874111ba1bd8a557975b41b89db49a5 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Sun, 2 Nov 2025 22:23:00 -0800
Subject: [PATCH 1/2] Fix errors for raise NotImplemented

---
 mypy/checker.py                            | 17 ++++++++++++-----
 test-data/unit/check-statements.test       |  2 +-
 test-data/unit/fixtures/notimplemented.pyi | 13 ++++++++++---
 3 files changed, 23 insertions(+), 9 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 63e128f78310..39885dfb7555 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -4959,10 +4959,10 @@ def check_return_stmt(self, s: ReturnStmt) -> None:
                     )
                 # Treat NotImplemented as having type Any, consistent with its
                 # definition in typeshed prior to python/typeshed#4222.
-                if (
-                    isinstance(typ, Instance)
-                    and typ.type.fullname == "builtins._NotImplementedType"
-                ):
+                if isinstance(typ, Instance) and typ.type.fullname in {
+                    "builtins._NotImplementedType",
+                    "types.NotImplementedType",
+                }:
                     typ = AnyType(TypeOfAny.special_form)
 
                 if defn.is_async_generator:
@@ -5121,7 +5121,14 @@ def type_check_raise(self, e: Expression, s: RaiseStmt, optional: bool = False)
             # https://github.com/python/mypy/issues/11089
             self.expr_checker.check_call(typ, [], [], e)
 
-        if isinstance(typ, Instance) and typ.type.fullname == "builtins._NotImplementedType":
+        if (
+            isinstance(typ, Instance)
+            and typ.type.fullname in {"builtins._NotImplementedType", "types.NotImplementedType"}
+        ) or (
+            isinstance(e, CallExpr)
+            and isinstance(e.callee, RefExpr)
+            and e.callee.fullname in {"builtins.NotImplemented"}
+        ):
             self.fail(
                 message_registry.INVALID_EXCEPTION.with_additional_msg(
                     '; did you mean "NotImplementedError"?'
diff --git a/test-data/unit/check-statements.test b/test-data/unit/check-statements.test
index 9ab68b32472d..d50a62a8dad6 100644
--- a/test-data/unit/check-statements.test
+++ b/test-data/unit/check-statements.test
@@ -523,7 +523,7 @@ if object():
 if object():
     raise NotImplemented    # E: Exception must be derived from BaseException; did you mean "NotImplementedError"?
 if object():
-    raise NotImplemented()  # E: NotImplemented? not callable
+    raise NotImplemented()  # E: Exception must be derived from BaseException; did you mean "NotImplementedError"?
 [builtins fixtures/notimplemented.pyi]
 
 [case testTryFinallyStatement]
diff --git a/test-data/unit/fixtures/notimplemented.pyi b/test-data/unit/fixtures/notimplemented.pyi
index 92edf84a7fd1..c9e58f099477 100644
--- a/test-data/unit/fixtures/notimplemented.pyi
+++ b/test-data/unit/fixtures/notimplemented.pyi
@@ -10,9 +10,16 @@ class bool: pass
 class int: pass
 class str: pass
 class dict: pass
+class tuple: pass
+class ellipsis: pass
 
-class _NotImplementedType(Any):
-    __call__: NotImplemented  # type: ignore
-NotImplemented: _NotImplementedType
+import sys
+
+if sys.version_info >= (3, 10):  # type: ignore
+    from types import NotImplementedType
+    NotImplemented: NotImplementedType
+else:
+    class _NotImplementedType(Any): ...
+    NotImplemented: _NotImplementedType
 
 class BaseException: pass

From 1d8482b51f1c885dbdf600d52f3a7ff8a2c564d2 Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Mon, 3 Nov 2025 18:26:57 -0800
Subject: [PATCH 2/2] .

---
 mypy/checker.py | 6 ++----
 mypy/types.py   | 2 ++
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/mypy/checker.py b/mypy/checker.py
index 39885dfb7555..1e0a1f311852 100644
--- a/mypy/checker.py
+++ b/mypy/checker.py
@@ -197,6 +197,7 @@
 from mypy.types import (
     ANY_STRATEGY,
     MYPYC_NATIVE_INT_NAMES,
+    NOT_IMPLEMENTED_TYPE_NAMES,
     OVERLOAD_NAMES,
     AnyType,
     BoolTypeQuery,
@@ -4959,10 +4960,7 @@ def check_return_stmt(self, s: ReturnStmt) -> None:
                     )
                 # Treat NotImplemented as having type Any, consistent with its
                 # definition in typeshed prior to python/typeshed#4222.
-                if isinstance(typ, Instance) and typ.type.fullname in {
-                    "builtins._NotImplementedType",
-                    "types.NotImplementedType",
-                }:
+                if isinstance(typ, Instance) and typ.type.fullname in NOT_IMPLEMENTED_TYPE_NAMES:
                     typ = AnyType(TypeOfAny.special_form)
 
                 if defn.is_async_generator:
diff --git a/mypy/types.py b/mypy/types.py
index 426d560c2bf7..df854325a64b 100644
--- a/mypy/types.py
+++ b/mypy/types.py
@@ -188,6 +188,8 @@
 
 ELLIPSIS_TYPE_NAMES: Final = ("builtins.ellipsis", "types.EllipsisType")
 
+NOT_IMPLEMENTED_TYPE_NAMES: Final = ("builtins._NotImplementedType", "types.NotImplementedType")
+
 # A placeholder used for Bogus[...] parameters
 _dummy: Final[Any] = object()