At the PythonLabs meeting someone mentioned it would make Jim really

happy if one could delete the __dict__ attribute of an instance.  I
love to make Jim happy, so here goes...

- New-style objects now support deleting their __dict__.  This is for
  all intents and purposes equivalent to assigning a brand new empty
  dictionary, but saves space if the object is not used further.

Lib/test/test_descr.py

@@ -2261,12 +2261,7 @@ def setdict():
     cant(a, None)
     cant(a, [])
     cant(a, 1)
-    try:
-        del a.__dict__
-    except TypeError:
-        pass
-    else:
-        raise TestFailed, "shouldn't allow del %r.__dict__" % (a)
+    del a.__dict__ # Deleting __dict__ is allowed
     # Classes don't allow __dict__ assignment
     cant(C, {})
 

Misc/NEWS

@@ -30,6 +30,10 @@ Type/class unification and new-style classes
   dict.__hash__ and list.__hash__ now raises the same TypeError
   (previously, these were the same as object.__hash__).
 
+- New-style objects now support deleting their __dict__.  This is for
+  all intents and purposes equivalent to assigning a brand new empty
+  dictionary, but saves space if the object is not used further.
+
 Core and builtins
 
 Extension modules

Objects/typeobject.c

@@ -812,13 +812,13 @@ subtype_setdict(PyObject *obj, PyObject *value, void *context)
 				"This object has no __dict__");
 		return -1;
 	}
-	if (value == NULL || !PyDict_Check(value)) {
+	if (value != NULL && !PyDict_Check(value)) {
 		PyErr_SetString(PyExc_TypeError,
 				"__dict__ must be set to a dictionary");
 		return -1;
 	}
 	dict = *dictptr;
-	Py_INCREF(value);
+	Py_XINCREF(value);
 	*dictptr = value;
 	Py_XDECREF(dict);
 	return 0;