From de5d514e649729a1f9e6f3e132d8ffb872d38b08 Mon Sep 17 00:00:00 2001
From: Nate Soares <nate@so8r.es>
Date: Mon, 6 Mar 2017 14:56:28 -0800
Subject: [PATCH 1/3] Make ABCMeta.__new__ pass **kwargs to type.__new__

Many metaclasses in the standard library don't play nice with
__init_subclass__. This bug makes ABCMeta in particular with
__init_subclass__, which is an 80/20 solution for me personally.
AFAICT, a general solution to this problem requires updating all
metaclasses in the standard library to make sure they pass **kwargs to
type.__new__, whereas this PR only fixes ABCMeta. For context, see
https://bugs.python.org/issue29581.
---
 Lib/abc.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/Lib/abc.py b/Lib/abc.py
index 1cbf96a61f238f6..43a34a0bbded786 100644
--- a/Lib/abc.py
+++ b/Lib/abc.py
@@ -129,8 +129,8 @@ class ABCMeta(type):
     #       external code.
     _abc_invalidation_counter = 0
 
-    def __new__(mcls, name, bases, namespace):
-        cls = super().__new__(mcls, name, bases, namespace)
+    def __new__(mcls, name, bases, namespace, **kwargs):
+        cls = super().__new__(mcls, name, bases, namespace, **kwargs)
         # Compute set of abstract method names
         abstracts = {name
                      for name, value in namespace.items()

From 87dc688aa09b56f22f3566956ec95b79d2ce4c1d Mon Sep 17 00:00:00 2001
From: Nate Soares <nate@so8r.es>
Date: Mon, 6 Mar 2017 15:24:52 -0800
Subject: [PATCH 2/3] added a test combining ABCMeta and __init_subclass__

---
 Lib/test/test_abc.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index e1765f0d5a54cba..4bc838200413af8 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -404,5 +404,17 @@ class C(A, B):
         self.assertEqual(B.counter, 1)
 
 
+class TestABCWithInitSubclass(unittest.TestCase):
+    def test_works_with_init_subclass(self):
+        saved_kwargs = {}
+        class ReceivesClassKwargs:
+            def __init_subclass__(cls, **kwargs):
+                super().__init_subclass__()
+                saved_kwargs.update(kwargs)
+        class Receiver(ReceivesClassKwargs, abc.ABC, x=1, y=2, z=3):
+            pass
+        self.assertEqual(saved_kwargs, dict(x=1, y=2, z=3))
+
+
 if __name__ == "__main__":
     unittest.main()

From f2b4f4ba8ca95b92c26fbe5a732fcb3312ebf53b Mon Sep 17 00:00:00 2001
From: Nate Soares <nate@so8r.es>
Date: Tue, 14 Mar 2017 21:15:06 -0700
Subject: [PATCH 3/3] Added NEWS item

---
 Misc/NEWS | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Misc/NEWS b/Misc/NEWS
index bcd049661edb1f2..5c9513f0a7c6815 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -714,6 +714,9 @@ Library
 - Issue #24142: Reading a corrupt config file left configparser in an
   invalid state.  Original patch by Florian Höch.
 
+- Issue #29581: ABCMeta.__new__ now accepts **kwargs, allowing abstract base
+  classes to use keyword parameters in __init_subclass__. Patch by Nate Soares.
+
 Windows
 -------