abstract_get_bases(): Clarify exactly what the return values and

states can be for this function, and ensure that only AttributeErrors
are masked.  Any other exception raised via the equivalent of
getattr(cls, '__bases__') should be propagated up.

abstract_issubclass(): If abstract_get_bases() returns NULL, we must
call PyErr_Occurred() to see if an exception is being propagated, and
return -1 or 0 as appropriate.  This is the specific fix for a problem
whereby if getattr(derived, '__bases__') raised an exception, an
"undetected error" would occur (under a debug build).  This nasty
situation was uncovered when writing a security proxy extension type
for the Zope3 project, where the security proxy raised a Forbidden
exception on getattr of __bases__.

PyObject_IsInstance(), PyObject_IsSubclass(): After both calls to
abstract_get_bases(), where we're setting the TypeError if the return
value is NULL, we must first check to see if an exception occurred,
and /not/ mask an existing exception.

Neil Schemenauer should double check that these changes don't break
his ExtensionClass examples (there aren't any test cases for those
examples and abstract_get_bases() was added by him in response to
problems with ExtensionClass).  Neil, please add test cases if
possible!

I belive this is a bug fix candidate for Python 2.2.2.
This commit is contained in:
Barry Warsaw 2002-04-23 22:45:44 +00:00
parent 3adf8d1dae
commit f16951cffe
1 changed files with 46 additions and 9 deletions

View File

@ -1861,6 +1861,32 @@ PyObject_CallFunctionObjArgs(PyObject *callable, ...)
/* isinstance(), issubclass() */
/* abstract_get_bases() has logically 4 return states, with a sort of 0th
* state that will almost never happen.
*
* 0. creating the __bases__ static string could get a MemoryError
* 1. getattr(cls, '__bases__') could raise an AttributeError
* 2. getattr(cls, '__bases__') could raise some other exception
* 3. getattr(cls, '__bases__') could return a tuple
* 4. getattr(cls, '__bases__') could return something other than a tuple
*
* Only state #3 is a non-error state and only it returns a non-NULL object
* (it returns the retrieved tuple).
*
* Any raised AttributeErrors are masked by clearing the exception and
* returning NULL. If an object other than a tuple comes out of __bases__,
* then again, the return value is NULL. So yes, these two situations
* produce exactly the same results: NULL is returned and no error is set.
*
* If some exception other than AttributeError is raised, then NULL is also
* returned, but the exception is not cleared. That's because we want the
* exception to be propagated along.
*
* Callers are expected to test for PyErr_Occurred() when the return value
* is NULL to decide whether a valid exception should be propagated or not.
* When there's no exception to propagate, it's customary for the caller to
* set a TypeError.
*/
static PyObject *
abstract_get_bases(PyObject *cls)
{
@ -1872,13 +1898,16 @@ abstract_get_bases(PyObject *cls)
if (__bases__ == NULL)
return NULL;
}
bases = PyObject_GetAttr(cls, __bases__);
if (bases == NULL || !PyTuple_Check(bases)) {
Py_XDECREF(bases);
if (bases == NULL) {
if (PyErr_ExceptionMatches(PyExc_AttributeError))
PyErr_Clear();
return NULL;
}
if (!PyTuple_Check(bases)) {
Py_DECREF(bases);
return NULL;
}
return bases;
}
@ -1895,9 +1924,11 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
return 1;
bases = abstract_get_bases(derived);
if (bases == NULL)
if (bases == NULL) {
if (PyErr_Occurred())
return -1;
return 0;
}
n = PyTuple_GET_SIZE(bases);
for (i = 0; i < n; i++) {
r = abstract_issubclass(PyTuple_GET_ITEM(bases, i), cls);
@ -1942,7 +1973,9 @@ PyObject_IsInstance(PyObject *inst, PyObject *cls)
else {
PyObject *cls_bases = abstract_get_bases(cls);
if (cls_bases == NULL) {
PyErr_SetString(PyExc_TypeError,
/* Do not mask errors. */
if (!PyErr_Occurred())
PyErr_SetString(PyExc_TypeError,
"isinstance() arg 2 must be a class or type");
return -1;
}
@ -1977,7 +2010,9 @@ PyObject_IsSubclass(PyObject *derived, PyObject *cls)
derived_bases = abstract_get_bases(derived);
if (derived_bases == NULL) {
PyErr_SetString(PyExc_TypeError,
/* Do not mask errors */
if (!PyErr_Occurred())
PyErr_SetString(PyExc_TypeError,
"issubclass() arg 1 must be a class");
return -1;
}
@ -1985,7 +2020,9 @@ PyObject_IsSubclass(PyObject *derived, PyObject *cls)
cls_bases = abstract_get_bases(cls);
if (cls_bases == NULL) {
PyErr_SetString(PyExc_TypeError,
/* Do not mask errors */
if (!PyErr_Occurred())
PyErr_SetString(PyExc_TypeError,
"issubclass() arg 2 must be a class");
return -1;
}