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authorBarry Warsaw <barry@python.org>2002-04-23 22:45:44 (GMT)
committerBarry Warsaw <barry@python.org>2002-04-23 22:45:44 (GMT)
commitf16951cffe9e4171769213bbe1aecec3d8f5200a (patch)
tree65880c11281cc4b26c89a05c0ad134da17280d30
parent3adf8d1daef8d323c405fd157e40cbae1d636c23 (diff)
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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.
-rw-r--r--Objects/abstract.c55
1 files changed, 46 insertions, 9 deletions
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 622e819..d10d9d4 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -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;
}