PEP 589: TypedDict field cannot be overwritten by inheritance (#1143)

pep-0589.rst

@@ -274,6 +274,34 @@ The TypedDict ``XYZ`` has three items: ``x`` (type ``int``), ``y``
 A TypedDict cannot inherit from both a TypedDict type and a
 non-TypedDict base class.
 
+Additional notes on TypedDict class inheritance:
+
+* Changing a field type of a parent TypedDict class in a subclass is not allowed.
+  Example::
+
+   class X(TypedDict):
+      x: str
+
+   class Y(X):
+      x: int  # Type check error: cannot overwrite TypedDict field "x"
+
+  In the example outlined above TypedDict class annotations returns
+  type ``str`` for key ``x``::
+
+   print(Y.__annotations__)  # {'x': <class 'str'>}
+
+
+* Multiple inheritance does not allow conflict types for the same name field::
+
+   class X(TypedDict):
+      x: int
+
+   class Y(TypedDict):
+      x: str
+
+   class XYZ(X, Y):  # Type check error: cannot overwrite TypedDict field "x" while merging
+      xyz: bool
+
 
 Totality
 --------