Updated docstring and error messages

Author: angela-tarantula

Lib/typing.py

@@ -3091,10 +3091,10 @@ def __new__(cls, name, bases, ns, total=True, closed=None,
         """
         for base in bases:
             if type(base) is not _TypedDictMeta and base is not Generic:
-                raise TypeError('cannot inherit from both a TypedDict type '
+                raise TypeError('Cannot inherit from both a TypedDict type '
                                 'and a non-TypedDict base class')
         if closed is not None and extra_items is not NoExtraItems:
-            raise TypeError(f"Cannot combine closed={closed!r} and extra_items")
+            raise TypeError(f"Cannot use both closed and extra_items")
 
         if any(issubclass(b, Generic) for b in bases):
             generic_base = (Generic,)
@@ -3274,6 +3274,26 @@ class DatabaseUser(TypedDict):
             id: ReadOnly[int]  # the "id" key must not be modified
             username: str      # the "username" key can be changed
 
+    The *closed* argument controls whether the TypedDict allows additional
+    non-required items during inheritance and assignability checks.
+    If closed=True, the TypedDict is closed to additional items::
+
+        Point2D = TypedDict('Point2D', {'x': int, 'y': int}, closed=True)
+        class Point3D(Point2D):
+            z: int  # Type checker error
+
+    Passing closed=False explicitly requests TypedDict's default open behavior.
+    If closed is not provided, the behavior is inherited from the superclass.
+
+    The *extra_items* argument can instead be used to specify the type of
+    additional non-required keys::
+
+        Point2D = TypedDict('Point2D', {'x': int, 'y': int}, extra_items=int)
+        class Point3D(Point2D):
+            z: int      # OK
+            label: str  # Type checker error
+
+    See PEP 728 for more information about closed and extra_items.
     """
     ns = {'__annotations__': dict(fields)}
     module = _caller()