Change issubclass() so that recursive tuples (directly or indirectly

containing class objects) are allowed as the second argument.
This makes issubclass() more similar to isinstance() where recursive
tuples are allowed too.

Lib/test/test_isinstance.py

@@ -165,6 +165,13 @@ class Super:
 class Child(Super):
     pass
 
+# new-style classes
+class NewSuper(object):
+    pass
+
+class NewChild(NewSuper):
+    pass
+
 
 
 class TestIsInstanceIsSubclass(unittest.TestCase):
@@ -225,7 +232,17 @@ class TestIsInstanceIsSubclass(unittest.TestCase):
         self.assertEqual(False, issubclass(Super, (Child,)))
         self.assertEqual(True, issubclass(Super, (Child, Super)))
         self.assertEqual(False, issubclass(Child, ()))
-        self.assertRaises(TypeError, issubclass, Child, ((Child,),))
+        self.assertEqual(True, issubclass(Super, (Child, (Super,))))
+
+        self.assertEqual(True, issubclass(NewChild, (NewChild,)))
+        self.assertEqual(True, issubclass(NewChild, (NewSuper,)))
+        self.assertEqual(False, issubclass(NewSuper, (NewChild,)))
+        self.assertEqual(True, issubclass(NewSuper, (NewChild, NewSuper)))
+        self.assertEqual(False, issubclass(NewChild, ()))
+        self.assertEqual(True, issubclass(NewSuper, (NewChild, (NewSuper,))))
+
+        self.assertEqual(True, issubclass(int, (long, (float, int))))
+        self.assertEqual(True, issubclass(str, (unicode, (Child, NewChild, basestring))))
 
 
 

Objects/abstract.c

@@ -2021,11 +2021,11 @@ PyObject_IsSubclass(PyObject *derived, PyObject *cls)
 			int i;
 			int n = PyTuple_GET_SIZE(cls);
 			for (i = 0; i < n; ++i) {
-				if (!check_class(PyTuple_GET_ITEM(cls, i),
-						"issubclass() arg 2 must be a class"
-						" or tuple of classes"))
-					return -1;
+				retval = PyObject_IsSubclass(derived, PyTuple_GET_ITEM(cls, i));
+				if (retval != 0) /* either found it, or got an error */
+					return retval;
 			}
+			return 0;
 		}
 		else {
 			if (!check_class(cls,

Objects/classobject.c

@@ -490,9 +490,10 @@ PyClass_IsSubclass(PyObject *class, PyObject *base)
 	if (PyTuple_Check(base)) {
 		n = PyTuple_GET_SIZE(base);
 		for (i = 0; i < n; i++) {
-			if (class == PyTuple_GET_ITEM(base, i))
+			if (PyClass_IsSubclass(class, PyTuple_GET_ITEM(base, i)))
 				return 1;
 		}
+		return 0;
 	}
 	if (class == NULL || !PyClass_Check(class))
 		return 0;