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/Include/stringobject.h	Sun Feb 25 17:56:27 2007 +0000
+++ b/Include/stringobject.h	Sun Feb 25 19:44:48 2007 +0000
@@ -55,7 +55,8 @@
 PyAPI_DATA(PyTypeObject) PyBaseString_Type;
 PyAPI_DATA(PyTypeObject) PyString_Type;
 
-#define PyString_Check(op) PyObject_TypeCheck(op, &PyString_Type)
+#define PyString_Check(op) \
+                 PyType_FastSubclass((op)->ob_type, Py_TPFLAGS_STRING_SUBCLASS)
 #define PyString_CheckExact(op) ((op)->ob_type == &PyString_Type)
 
 PyAPI_FUNC(PyObject *) PyString_FromStringAndSize(const char *, Py_ssize_t);