From a94e6272f16381349dbed74cdb738ec8ae23b4fe Mon Sep 17 00:00:00 2001
From: Serhiy Storchaka <storchaka@gmail.com>
Date: Sat, 4 Apr 2020 21:31:30 +0300
Subject: [PATCH] bpo-36517: Raise error on multiple inheritance with
 NamedTuple (GH-19363)

---
 Lib/test/test_typing.py                                    | 7 +++++++
 Lib/typing.py                                              | 3 +++
 .../next/Library/2020-04-04-17-49-39.bpo-36517.Ilj1IJ.rst  | 2 ++
 3 files changed, 12 insertions(+)
 create mode 100644 Misc/NEWS.d/next/Library/2020-04-04-17-49-39.bpo-36517.Ilj1IJ.rst

diff --git a/Lib/test/test_typing.py b/Lib/test/test_typing.py
index 8d6262b9c1b..3a0edb9e2d3 100644
--- a/Lib/test/test_typing.py
+++ b/Lib/test/test_typing.py
@@ -3626,6 +3626,13 @@ class XMethBad2(NamedTuple):
         return 'no chance for this as well'
 """)
 
+    def test_multiple_inheritance(self):
+        class A:
+            pass
+        with self.assertRaises(TypeError):
+            class X(NamedTuple, A):
+                x: int
+
     def test_namedtuple_keyword_usage(self):
         LocalEmployee = NamedTuple("LocalEmployee", name=str, age=int)
         nick = LocalEmployee('Nick', 25)
diff --git a/Lib/typing.py b/Lib/typing.py
index 53518830002..99355d00666 100644
--- a/Lib/typing.py
+++ b/Lib/typing.py
@@ -1728,6 +1728,9 @@ class NamedTupleMeta(type):
     def __new__(cls, typename, bases, ns):
         if ns.get('_root', False):
             return super().__new__(cls, typename, bases, ns)
+        if len(bases) > 1:
+            raise TypeError("Multiple inheritance with NamedTuple is not supported")
+        assert bases[0] is NamedTuple
         types = ns.get('__annotations__', {})
         nm_tpl = _make_nmtuple(typename, types.items())
         defaults = []
diff --git a/Misc/NEWS.d/next/Library/2020-04-04-17-49-39.bpo-36517.Ilj1IJ.rst b/Misc/NEWS.d/next/Library/2020-04-04-17-49-39.bpo-36517.Ilj1IJ.rst
new file mode 100644
index 00000000000..cd5c0d729f1
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-04-04-17-49-39.bpo-36517.Ilj1IJ.rst
@@ -0,0 +1,2 @@
+Multiple inheritance with :class:`typing.NamedTuple` now raises an error
+instead of silently ignoring other types.