Enhance issubclass() and PyObject_IsSubclass() so that a tuple is

supported as the second argument. This has the same meaning as
for isinstance(), i.e. issubclass(X, (A, B)) is equivalent
to issubclass(X, A) or issubclass(X, B). Compared to isinstance(),
this patch does not search the tuple recursively for classes, i.e.
any entry in the tuple that is not a class, will result in a
TypeError.

This closes SF patch #649608.

2 files changed, 49 insertions, 28 deletions

diff --git a/Objects/abstract.c b/Objects/abstract.c
index e77cde3..47d2f31 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -1914,6 +1914,15 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
 	if (derived == cls)
 		return 1;
 
+	if (PyTuple_Check(cls)) {
+		/* Not a general sequence -- that opens up the road to
+		   recursion and stack overflow. */
+		n = PyTuple_GET_SIZE(cls);
+		for (i = 0; i < n; i++) {
+			if (derived == PyTuple_GET_ITEM(cls, i))
+				return 1;
+		}
+	}
 	bases = abstract_get_bases(derived);
 	if (bases == NULL) {
 		if (PyErr_Occurred())
@@ -1932,6 +1941,20 @@ abstract_issubclass(PyObject *derived, PyObject *cls)
 	return r;
 }
 
+static int
+check_class(PyObject *cls, const char *error)
+{
+	PyObject *bases = abstract_get_bases(cls);
+	if (bases == NULL) {
+		/* Do not mask errors. */
+		if (!PyErr_Occurred())
+			PyErr_SetString(PyExc_TypeError, error);
+		return 0;
+	}
+	Py_DECREF(bases);
+	return -1;
+}
+
 int
 PyObject_IsInstance(PyObject *inst, PyObject *cls)
 {
@@ -1962,16 +1985,10 @@ PyObject_IsInstance(PyObject *inst, PyObject *cls)
 		return retval;
 	}
 	else {
-		PyObject *cls_bases = abstract_get_bases(cls);
-		if (cls_bases == NULL) {
-			/* Do not mask errors. */
-			if (!PyErr_Occurred())
-				PyErr_SetString(PyExc_TypeError,
-				"isinstance() arg 2 must be a class, type,"
-				" or tuple of classes and types");
+		if (!check_class(cls,
+			"isinstance() arg 2 must be a class, type,"
+			" or tuple of classes and types"))
 			return -1;
-		}
-		Py_DECREF(cls_bases);
 		if (__class__ == NULL) {
 			__class__ = PyString_FromString("__class__");
 			if (__class__ == NULL)
@@ -1997,28 +2014,25 @@ PyObject_IsSubclass(PyObject *derived, PyObject *cls)
 	int retval;
 
 	if (!PyClass_Check(derived) || !PyClass_Check(cls)) {
-		PyObject *derived_bases;
-		PyObject *cls_bases;
-
-		derived_bases = abstract_get_bases(derived);
-		if (derived_bases == NULL) {
-			/* Do not mask errors */
-			if (!PyErr_Occurred())
-				PyErr_SetString(PyExc_TypeError,
-					"issubclass() arg 1 must be a class");
+		if (!check_class(derived, "issubclass() arg 1 must be a class"))
 			return -1;
+
+		if (PyTuple_Check(cls)) {
+			int i;
+			int n = PyTuple_GET_SIZE(cls);
+			for (i = 0; i < n; ++i) {
+				if (!check_class(PyTuple_GET_ITEM(cls, i),
+						"issubclass() arg 2 must be a class"
+						" or tuple of classes"))
+					return -1;
+			}
 		}
-		Py_DECREF(derived_bases);
-
-		cls_bases = abstract_get_bases(cls);
-		if (cls_bases == NULL) {
-			/* Do not mask errors */
-			if (!PyErr_Occurred())
-				PyErr_SetString(PyExc_TypeError,
-					"issubclass() arg 2 must be a class");
-			return -1;
+		else {
+			if (!check_class(cls,
+					"issubclass() arg 2 must be a class"
+					" or tuple of classes"))
+				return -1;
 		}
-		Py_DECREF(cls_bases);
 
 		retval = abstract_issubclass(derived, cls);
 	}
diff --git a/Objects/classobject.c b/Objects/classobject.c
index f7b442a..f3b9873 100644
--- a/Objects/classobject.c
+++ b/Objects/classobject.c
@@ -487,6 +487,13 @@ PyClass_IsSubclass(PyObject *class, PyObject *base)
 	PyClassObject *cp;
 	if (class == base)
 		return 1;
+	if (PyTuple_Check(base)) {
+		n = PyTuple_GET_SIZE(base);
+		for (i = 0; i < n; i++) {
+			if (class == PyTuple_GET_ITEM(base, i))
+				return 1;
+		}
+	}
 	if (class == NULL || !PyClass_Check(class))
 		return 0;
 	cp = (PyClassObject *)class;