From 610a51f364f6cb5ffb5167d9bf4dcecc1815107c Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Sun, 17 May 2015 14:45:58 -0700
Subject: [PATCH] Issue #23757:  Only call the concrete list API for exact
 lists.

---
 Lib/test/seq_tests.py | 12 ++++++++++++
 Misc/NEWS             |  3 +++
 Objects/abstract.c    |  2 +-
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/Lib/test/seq_tests.py b/Lib/test/seq_tests.py
index 9834af118a5..24162494dd6 100644
--- a/Lib/test/seq_tests.py
+++ b/Lib/test/seq_tests.py
@@ -85,6 +85,14 @@ def itermulti(seqn):
     'Test multiple tiers of iterators'
     return chain(map(lambda x:x, iterfunc(IterGen(Sequence(seqn)))))
 
+class LyingTuple(tuple):
+    def __iter__(self):
+        yield 1
+
+class LyingList(list):
+    def __iter__(self):
+        yield 1
+
 class CommonTest(unittest.TestCase):
     # The type to be tested
     type2test = None
@@ -131,6 +139,10 @@ class CommonTest(unittest.TestCase):
             self.assertRaises(TypeError, self.type2test, IterNoNext(s))
             self.assertRaises(ZeroDivisionError, self.type2test, IterGenExc(s))
 
+        # Issue #23757
+        self.assertEqual(self.type2test(LyingTuple((2,))), self.type2test((1,)))
+        self.assertEqual(self.type2test(LyingList([2])), self.type2test([1]))
+
     def test_truth(self):
         self.assertFalse(self.type2test())
         self.assertTrue(self.type2test([42]))
diff --git a/Misc/NEWS b/Misc/NEWS
index e9b1461944b..2599b821d31 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -13,6 +13,9 @@ Core and Builtins
 - Issue #20274: Remove ignored and erroneous "kwargs" parameters from three
   METH_VARARGS methods on _sqlite.Connection.
 
+- Issue #23757:  PySequence_Tuple() incorrectly called the concrete list API
+  when the data was a list subclass.
+
 - Issue #24096: Make warnings.warn_explicit more robust against mutation of the
   warnings.filters list.
 
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 7e3121a932c..cabbaf5ba1c 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -1636,7 +1636,7 @@ PySequence_Tuple(PyObject *v)
         Py_INCREF(v);
         return v;
     }
-    if (PyList_Check(v))
+    if (PyList_CheckExact(v))
         return PyList_AsTuple(v);
 
     /* Get iterator. */