From d632664a33c6003607122c3ae542d5db66cb77b6 Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Wed, 27 Jan 2010 02:25:58 +0000
Subject: [PATCH] Merged revisions 77789 via svnmerge from
 svn+ssh://pythondev@svn.python.org/python/trunk

........
  r77789 | benjamin.peterson | 2010-01-26 20:16:42 -0600 (Tue, 26 Jan 2010) | 1 line

  raise a clear TypeError when trying to register a non-class
........
---
 Lib/abc.py           | 2 +-
 Lib/test/test_abc.py | 6 ++++++
 Misc/NEWS            | 2 ++
 3 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/Lib/abc.py b/Lib/abc.py
index f9b49ac3d1c..0f980363046 100644
--- a/Lib/abc.py
+++ b/Lib/abc.py
@@ -94,7 +94,7 @@ def __new__(mcls, name, bases, namespace):
 
     def register(cls, subclass):
         """Register a virtual subclass of an ABC."""
-        if not isinstance(cls, type):
+        if not isinstance(subclass, type):
             raise TypeError("Can only register classes")
         if issubclass(subclass, cls):
             return  # Already a subclass
diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
index c9deb4b9677..a6e7062418f 100644
--- a/Lib/test/test_abc.py
+++ b/Lib/test/test_abc.py
@@ -139,6 +139,12 @@ class C(A):
         self.assertRaises(RuntimeError, C.register, A)  # cycles not allowed
         C.register(B)  # ok
 
+    def test_register_non_class(self):
+        class A(metaclass=abc.ABCMeta):
+            pass
+        self.assertRaisesRegexp(TypeError, "Can only register classes",
+                                A.register, 4)
+
     def test_registration_transitiveness(self):
         class A(metaclass=abc.ABCMeta):
             pass
diff --git a/Misc/NEWS b/Misc/NEWS
index cf777df46f3..1e0ae084a32 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -234,6 +234,8 @@ C-API
 Library
 -------
 
+- Issue #7792: Registering non-classes to ABCs raised an obscure error.
+
 - Issue #7785: Don't accept bytes in FileIO.write().
 
 - Removed the functions 'verify' and 'vereq' from Lib/test/support.py.