GH-127058: Make `PySequence_Tuple` safer and probably faster. (#127758)

* Use a small buffer, then list when constructing a tuple from an arbitrary sequence.

1 files changed, 25 insertions, 0 deletions

diff --git a/Lib/test/test_capi/test_tuple.py b/Lib/test/test_capi/test_tuple.py
index e6b49ca..6349467 100644
--- a/Lib/test/test_capi/test_tuple.py
+++ b/Lib/test/test_capi/test_tuple.py
@@ -1,5 +1,6 @@
 import unittest
 import sys
+import gc
 from collections import namedtuple
 from test.support import import_helper
 
@@ -257,5 +258,29 @@ class CAPITest(unittest.TestCase):
         self.assertRaises(SystemError, resize, [1, 2, 3], 0, False)
         self.assertRaises(SystemError, resize, NULL, 0, False)
 
+    def test_bug_59313(self):
+        # Before 3.14, the C-API function PySequence_Tuple
+        # would create incomplete tuples which were visible to
+        # the cycle GC, and this test would crash the interpeter.
+        TAG = object()
+        tuples = []
+
+        def referrer_tuples():
+            return [x for x in gc.get_referrers(TAG)
+                if isinstance(x, tuple)]
+
+        def my_iter():
+            nonlocal tuples
+            yield TAG    # 'tag' gets stored in the result tuple
+            tuples += referrer_tuples()
+            for x in range(10):
+                tuples += referrer_tuples()
+                # Prior to 3.13 would raise a SystemError when the tuple needs to be resized
+                yield x
+
+        self.assertEqual(tuple(my_iter()), (TAG, *range(10)))
+        self.assertEqual(tuples, [])
+
+
 if __name__ == "__main__":
     unittest.main()