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