Merged revisions 77791 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/branches/py3k

................
  r77791 | benjamin.peterson | 2010-01-26 20:25:58 -0600 (Tue, 26 Jan 2010) | 9 lines

  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

@@ -94,7 +94,7 @@ 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

@@ -139,6 +139,12 @@ 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(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

Misc/NEWS

@@ -73,6 +73,8 @@ Core and Builtins
 Library
 -------
 
+- Issue #7792: Registering non-classes to ABCs raised an obscure error.
+
 - Issue #7785: Don't accept bytes in FileIO.write().
 
 - Issue #7773: Fix an UnboundLocalError in platform.linux_distribution() when