Merged revisions 77788-77789 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

........
  r77788 | benjamin.peterson | 2010-01-26 20:15:28 -0600 (Tue, 26 Jan 2010) | 1 line

  for UserDict to be compatible with abcs, it must subclass object
........
  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/UserDict.py

@@ -1,6 +1,6 @@
 """A more or less complete user-defined wrapper around dictionary objects."""
 
-class UserDict:
+class UserDict(object):
     def __init__(self, dict=None, **kwargs):
         self.data = {}
         if dict is not None:

Lib/abc.py

@@ -96,7 +96,7 @@ class ABCMeta(type):
 
     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

Lib/test/test_abc.py

@@ -149,6 +149,11 @@ class TestABC(unittest.TestCase):
         self.assertRaises(RuntimeError, C.register, A)  # cycles not allowed
         C.register(B)  # ok
 
+    def test_register_non_class(self):
+        class A(object):
+            __metaclass__ = abc.ABCMeta
+        self.assertRaises(TypeError, A.register, 4)
+
     def test_registration_transitiveness(self):
         class A:
             __metaclass__ = abc.ABCMeta

Misc/NEWS

@@ -53,6 +53,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #7792: Registering non-classes to ABCs raised an obscure error.
+
 - Issue #7773: Fix an UnboundLocalError in platform.linux_distribution() when
   the release file is empty.