gh-157176: Make time.struct_time type immutable (#157179)

Co-authored-by: Victor Stinner <vstinner@python.org>

Author: ashm-dev

Lib/test/test_structseq.py

@@ -6,6 +6,7 @@
 import textwrap
 import time
 import unittest
+from test import support
 from test.support import script_helper
 
 
@@ -351,9 +352,9 @@ def test_reference_cycle(self):
         # was cleared first, the structseq instance would crash in the
         # destructor.
         script_helper.assert_python_ok("-c", textwrap.dedent(r"""
-            import time
-            t = time.gmtime()
-            type(t).refcyle = t
+            import os
+            t = os.stat('.')
+            type(t).refcycle = t
         """))
 
     def test_replace_gc_tracked(self):
@@ -365,5 +366,8 @@ def test_replace_gc_tracked(self):
 
         self.assertTrue(gc.is_tracked(replaced_struct))
 
+    def test_struct_time_type_immutable(self):
+        support.check_immutable_type(self, type(time.gmtime()))
+
 if __name__ == "__main__":
     unittest.main()

Misc/NEWS.d/next/Core_and_Builtins/2026-09-08-15-55-00.gh-issue-157176.yZ8a1B.rst

@@ -0,0 +1 @@
+Make the :class:`time.struct_time` type immutable to prevent reference cycles between the type and its instances. Patch by Shamil Abdulaev.

Modules/timemodule.c

@@ -5,6 +5,7 @@
 #include "pycore_moduleobject.h"  // _PyModule_GetState()
 #include "pycore_namespace.h"     // _PyNamespace_New()
 #include "pycore_runtime.h"       // _Py_ID()
+#include "pycore_structseq.h"     // _PyStructSequence_NewType()
 #include "pycore_time.h"          // _PyTimeFraction
 
 #include <time.h>                 // clock()
@@ -2164,7 +2165,8 @@ time_exec(PyObject *module)
     }
 
     // struct_time type
-    state->struct_time_type = PyStructSequence_NewType(&struct_time_type_desc);
+    state->struct_time_type = _PyStructSequence_NewType(
+        &struct_time_type_desc, Py_TPFLAGS_IMMUTABLETYPE);
     if (state->struct_time_type == NULL) {
         return -1;
     }