From 718fb7491648ac5a1fb6eb22916d8aecf450aab4 Mon Sep 17 00:00:00 2001
From: Sergey <sergunya@outlook.com>
Date: Sun, 11 Aug 2019 21:21:31 +0300
Subject: [PATCH] PEP 589: TypedDict field cannot be overwritten by inheritance
 (#1143)

---
 pep-0589.rst | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/pep-0589.rst b/pep-0589.rst
index 94f7c2fd8..a007adfa1 100644
--- a/pep-0589.rst
+++ b/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
 --------