From 51dbc9a4ad272d832dfd5265cc3161cbb658aecb Mon Sep 17 00:00:00 2001
From: Raymond Hettinger <python@rcn.com>
Date: Sun, 17 May 2015 14:37:39 -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 f5e4e0ef55..f4673d48af 100644
--- a/Lib/test/seq_tests.py
+++ b/Lib/test/seq_tests.py
@@ -84,6 +84,14 @@ def itermulti(seqn):
     'Test multiple tiers of iterators'
     return chain(imap(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
@@ -130,6 +138,10 @@ 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 ab36ec45a9..c9b0dbefcd 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -51,6 +51,9 @@ Core and Builtins
 
 - Issue #23971:  Fix underestimated presizing in dict.fromkeys().
 
+- Issue #23757:  PySequence_Tuple() incorrectly called the concrete list API
+  when the data was a list subclass.
+
 - Issue #20274: Remove ignored and erroneous "kwargs" parameters from three
   METH_VARARGS methods on _sqlite.Connection.
 
diff --git a/Objects/abstract.c b/Objects/abstract.c
index 64a1a381e1..6e289eff6e 100644
--- a/Objects/abstract.c
+++ b/Objects/abstract.c
@@ -2169,7 +2169,7 @@ PySequence_Tuple(PyObject *v)
         Py_INCREF(v);
         return v;
     }
-    if (PyList_Check(v))
+    if (PyList_CheckExact(v))
         return PyList_AsTuple(v);
 
     /* Get iterator. */
-- 
2.50.1