A long time ago I wrote to Guido suggesting that I might like to submit
some patches to improve the comprehensibility of the Python source. He
was receptive, so my first one is attached (I will also post to the SF
patch manager). I did this in an effort to stop replicating the effort
of understanding how the new descriptor mechanism works on types. I'm
also testing the waters a bit, here: I hope it looks like an improvement
to people, but please let me know if it does not.
Regards,
Dave
--- typeobject.c Mon Dec 17 12:14:22 2001
+++ typeobject.c.new Thu Mar 28 13:46:03 2002
@@ -1186,8 +1186,8 @@
type_getattro(PyTypeObject *type, PyObject *name)
{
PyTypeObject *metatype = type->ob_type;
- PyObject *descr, *res;
- descrgetfunc f;
+ PyObject *meta_attribute, *attribute;
+ descrgetfunc meta_get;
/* Initialize this type (we'll assume the metatype is initialized) */
if (type->tp_dict == NULL) {
@@ -1195,34 +1195,50 @@
return NULL;
}
- /* Get a descriptor from the metatype */
- descr = _PyType_Lookup(metatype, name);
- f = NULL;
- if (descr != NULL) {
- f = descr->ob_type->tp_descr_get;
- if (f != NULL && PyDescr_IsData(descr))
- return f(descr,
- (PyObject *)type, (PyObject *)metatype);
- }
+ /* No readable descriptor found yet */
+ meta_get = NULL;
+
+ /* Look for the attribute in the metatype */
+ meta_attribute = _PyType_Lookup(metatype, name);
- /* Look in tp_dict of this type and its bases */
- res = _PyType_Lookup(type, name);
- if (res != NULL) {
- f = res->ob_type->tp_descr_get;
- if (f != NULL)
- return f(res, (PyObject *)NULL, (PyObject *)type);
- Py_INCREF(res);
- return res;
+ if (meta_attribute != NULL) {
+ meta_get = meta_attribute->ob_type->tp_descr_get;
+
+ if (meta_get != NULL && PyDescr_IsData(meta_attribute)) {
+ /* Data descriptors implement tp_descr_set to intercept
+ * writes. Assume the attribute is not overridden in
+ * type's tp_dict (and bases): call the descriptor now.
+ */
+ return meta_get(meta_attribute,
+ (PyObject *)type, (PyObject *)metatype);
+ }
}
- /* Use the descriptor from the metatype */
- if (f != NULL) {
- res = f(descr, (PyObject *)type, (PyObject *)metatype);
- return res;
+ /* No data descriptor found on metatype. Look in tp_dict of this
+ * type and its bases */
+ attribute = _PyType_Lookup(type, name);
+ if (attribute != NULL) {
+ /* Implement descriptor functionality, if any */
+ descrgetfunc local_get = attribute->ob_type->tp_descr_get;
+ if (local_get != NULL) {
+ /* NULL 2nd argument indicates the descriptor was found on
+ * the target object itself (or a base) */
+ return local_get(attribute, (PyObject *)NULL, (PyObject *)type);
+ }
+
+ Py_INCREF(attribute);
+ return attribute;
}
- if (descr != NULL) {
- Py_INCREF(descr);
- return descr;
+
+ /* No attribute found in local __dict__ (or bases): use the
+ * descriptor from the metatype, if any */
+ if (meta_get != NULL)
+ return meta_get(meta_attribute, (PyObject *)type, (PyObject
*)metatype);
+
+ /* If an ordinary attribute was found on the metatype, return it
now. */
+ if (meta_attribute != NULL) {
+ Py_INCREF(meta_attribute);
+ return meta_attribute;
}
/* Give up */
+---------------------------------------------------------------+
David Abrahams
C++ Booster (http://www.boost.org) O__ ==
Pythonista (http://www.python.org) c/ /'_ ==
resume: http://users.rcn.com/abrahams/resume.html (*) \(*) ==
email: david.abrahams@rcn.com
+---------------------------------------------------------------+
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