From 7f67fbc76a4881c01f0ddeb6fd26da8ce7806215 Mon Sep 17 00:00:00 2001 From: Jelle Zijlstra Date: Tue, 20 Oct 2026 10:16:11 -0700 Subject: [PATCH] gh-159739: Preserve the full maxlen when copying deque subclasses (GH-159765) (cherry picked from commit e3c395542adebfbca1f54379065c15380ac5e182) Co-authored-by: Jelle Zijlstra Co-authored-by: Jelle Zijlstra --- Lib/test/test_deque.py | 6 ++++++ .../Library/2026-10-19-20-38-17.gh-issue-159739.ff088c.rst | 1 + Modules/_collectionsmodule.c | 2 +- 3 files changed, 8 insertions(+), 1 deletion(-) create mode 100644 Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.ff088c.rst diff --git a/Lib/test/test_deque.py b/Lib/test/test_deque.py index 3c45032cda9138..0102f203340bd9 100644 --- a/Lib/test/test_deque.py +++ b/Lib/test/test_deque.py @@ -810,6 +810,12 @@ def __iter__(self): class TestSubclass(unittest.TestCase): + def test_copy_maxlen(self): + original = Deque('abc', maxlen=support.MAX_Py_ssize_t) + copied = original.copy() + self.assertEqual(copied, original) + self.assertEqual(copied.maxlen, original.maxlen) + def test_basics(self): d = Deque(range(25)) d.__init__(range(200)) diff --git a/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.ff088c.rst b/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.ff088c.rst new file mode 100644 index 00000000000000..af8b06fecbfc3f --- /dev/null +++ b/Misc/NEWS.d/next/Library/2026-10-19-20-38-17.gh-issue-159739.ff088c.rst @@ -0,0 +1 @@ +Fix copying :class:`collections.deque` subclasses with a large maximum length. diff --git a/Modules/_collectionsmodule.c b/Modules/_collectionsmodule.c index e48fe39dda6a09..8e081f51afae93 100644 --- a/Modules/_collectionsmodule.c +++ b/Modules/_collectionsmodule.c @@ -645,7 +645,7 @@ deque_copy_impl(dequeobject *deque) result = PyObject_CallOneArg((PyObject *)(Py_TYPE(deque)), (PyObject *)deque); else - result = PyObject_CallFunction((PyObject *)(Py_TYPE(deque)), "Oi", + result = PyObject_CallFunction((PyObject *)(Py_TYPE(deque)), "On", deque, old_deque->maxlen, NULL); if (result != NULL && !PyObject_TypeCheck(result, state->deque_type)) { PyErr_Format(PyExc_TypeError,