Fix the Python property class in a comment right.

Objects/descrobject.c

@@ -911,21 +911,22 @@ PyWrapper_New(PyObject *d, PyObject *self)
             self.__doc__ = doc
 
         def __get__(self, inst, type=None):
-	    if self.__get is NULL:
+            if self.__get is None:
                 raise AttributeError, "unreadable attribute"
             if inst is None:
                 return self
             return self.__get(inst)
 
         def __set__(self, inst, value):
-	    if value is None:
-	    	if self.__del is None:
-	    	    raise AttributeError, "can't delete attribute"
-	    	return self.__del(inst)
-	    else:
             if self.__set is None:
                 raise AttributeError, "can't set attribute"
             return self.__set(inst, value)
+
+        def __delete__(self, inst):
+            if self.__del is None:
+                raise AttributeError, "can't delete attribute"
+            return self.__del(inst)
+
 */
 
 typedef struct {