Variation of patch # 1624059 to speed up checking if an object is a subclass of some of the common builtin types. Use a bit in tp_flags for each common builtin type. Check the bit to determine if any instance is a subclass of these common types. The check avoids a function call and O(n) search of the base classes. The check is done in the various Py*_Check macros rather than calling PyType_IsSubtype(). All the bits are set in tp_flags when the type is declared in the Objects/*object.c files because PyType_Ready() is not called for all the types. Should PyType_Ready() be called for all types? If so and the change is made, the changes to the Objects/*object.c files can be reverted (remove setting the tp_flags). Objects/typeobject.c would also have to be modified to add conditions for Py*_CheckExact() in addition to each the PyType_IsSubtype check.

--- a/Objects/stringobject.c	Sun Feb 25 17:56:27 2007 +0000
+++ b/Objects/stringobject.c	Sun Feb 25 19:44:48 2007 +0000
@@ -4017,7 +4017,7 @@
 	0,					/* tp_setattro */
 	&string_as_buffer,			/* tp_as_buffer */
 	Py_TPFLAGS_DEFAULT | Py_TPFLAGS_CHECKTYPES |
-		Py_TPFLAGS_BASETYPE,		/* tp_flags */
+		Py_TPFLAGS_BASETYPE | Py_TPFLAGS_STRING_SUBCLASS,		/* tp_flags */
 	string_doc,				/* tp_doc */
 	0,					/* tp_traverse */
 	0,					/* tp_clear */