this bug was fixed in python2.5, but it's worth adding
to 2.4.4.

metaclasses can return an "insane" mro, which confuses
the PyXXX_Check checks, and causes memory corruption.

Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310
32 bit (Intel)] on win32
Type "help", "copyright", "credits" or "license" for
more information.
>>> class crasher(object):
...     class __metaclass__(type):
...             def mro(self):
...                     return (str, int, list)
...
>>> c = crasher("hello")
>>> c # a very strange object
''
>>> dir(c)
[]
>>> c.append(5)
# <access violation - program crashes>

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Can you please provide a reference to the original bug, or
to the revision that fixes the bug in 2.5?
+

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i never managed working with svn's or cvs's... i can point
you to the official source distribution of 2.4.2:

file: typeobject.c
function: static int mro_internal(PyTypeObject *type)
+-+-+-+-+-+-+-+-
		mro = lookup_method((PyObject *)type, "mro", &mro_str);
		if (mro == NULL)
			return -1;
		result = PyObject_CallObject(mro, NULL);
		Py_DECREF(mro);
	}
	if (result == NULL)
		return -1;
	tuple = PySequence_Tuple(result);
+-+-+-+-+-+-+-+-+-

python 2.5 (release) added the following check:
+-+-+-+-+-+-+-+-+-

			if (!PyType_IsSubtype(solid, solid_base(t))) {
				PyErr_Format(PyExc_TypeError,
		     "mro() returned base with unsuitable layout ('%.500s')",
					     t->tp_name);
+-+-+-+-+-+-+-+-+-


that's the best i can do, sorry

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This bugfix didn't make it into Python 2.4.4, and Anthony
Baxter suggests there probably won't be a 2.4.5 release, so
I'm closing this bug.  Sorry it didn't work out.