berkerpeksag · Aug 20, 2018 · Aug 20, 2018 · Aug 20, 2018 · Aug 20, 2018 · Aug 20, 2018
diff --git a/Lib/test/test_abc.py b/Lib/test/test_abc.py
@@ -410,6 +410,13 @@ class C:
             with self.assertRaises(TypeError):
                 issubclass(C(), A)
 
+            # bpo-34441: Check that issubclass() doesn't crash on bogus classes
+            class S(metaclass=abc_ABCMeta):
+                __subclasses__ = None
+
+            with self.assertRaises(TypeError):
+                issubclass(int, S)
+
         def test_all_new_methods_are_called(self):
             class A(metaclass=abc_ABCMeta):
                 pass

diff --git a/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst b/Misc/NEWS.d/next/Library/2018-08-20-16-48-32.bpo-34441._zx9lU.rst
@@ -0,0 +1,2 @@
+Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__`` is passed as the
+second argument to ``issubclass()``.
diff --git a/Modules/_abc.c b/Modules/_abc.c
@@ -665,6 +665,9 @@ _abc__abc_subclasscheck_impl(PyObject *module, PyObject *self,
 
     /* 6. Check if it's a subclass of a subclass (recursive). */
     subclasses = PyObject_CallMethod(self, "__subclasses__", NULL);
+    if (subclasses == NULL) {
+        goto end;
+    }
     if (!PyList_Check(subclasses)) {
         PyErr_SetString(PyExc_TypeError, "__subclasses__() must return a list");
         goto end;
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		Fix crash when an ``ABC``-derived class with non-callable ``__subclasses__`` is passed as the
		second argument to ``issubclass()``.
berkerpeksag Aug 20, 2018 Copy link Copy Markdown Member Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. ``issubclass()`` -> :func:`issubclass` berkerpeksag Aug 20, 2018 Copy link Copy Markdown Member Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Please add "Patch by Your Name." and wrap lines at 80 chars. izbyshev Aug 20, 2018 Copy link Copy Markdown Contributor Author Choose a reason for hiding this comment The reason will be displayed to describe this comment to others. Learn more. Fixed, thank you.