commit a7f929db605326da452fbdeebfe341afa9316d25
author Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> Sun Feb 17 15:33:04 2019 -0800
committer GitHub <noreply@github.com> Sun Feb 17 15:33:04 2019 -0800
tree 56b8fb61a61df34a2820591d9b04f88126df921f
parent 6f352199e4447764bc472e34352d0dff4db8a52d

bpo-35992: Use PySequence_GetItem only if sq_item is not NULL (GH-11857)


Not using `__class_getitem__()` fallback if there is a non-subcriptable metaclass was caused by a certain asymmetry between how `PySequenceMethods` and `PyMappingMethods` are used in `PyObject_GetItem`. This PR removes this asymmetry. No tests failed, so I assume it was not intentional.
(cherry picked from commit ac28147e78c45a6217d348ce90ca5281d91f676f)

Co-authored-by: Ivan Levkivskyi <levkivskyi@gmail.com>

Objects/abstract.c

diff --git a/Objects/abstract.c b/Objects/abstract.c
index 2d48a11..9416df4 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -143,6 +143,7 @@
 PyObject_GetItem(PyObject *o, PyObject *key)
 {
     PyMappingMethods *m;
+    PySequenceMethods *ms;
 
     if (o == NULL || key == NULL) {
         return null_error();
@@ -155,7 +156,8 @@
         return item;
     }
 
-    if (o->ob_type->tp_as_sequence) {
+    ms = o->ob_type->tp_as_sequence;
+    if (ms && ms->sq_item) {
         if (PyIndex_Check(key)) {
             Py_ssize_t key_value;
             key_value = PyNumber_AsSsize_t(key, PyExc_IndexError);
@@ -163,9 +165,10 @@
                 return NULL;
             return PySequence_GetItem(o, key_value);
         }
-        else if (o->ob_type->tp_as_sequence->sq_item)
+        else {
             return type_error("sequence index must "
                               "be integer, not '%.200s'", key);
+        }
     }
 
     if (PyType_Check(o)) {