python
@@ -41,6 +41,7 @@ extern PyStatus _Py_HashRandomization_Init(const PyConfig *);
 
 extern PyStatus _PyGC_Init(PyInterpreterState *interp);
 extern PyStatus _PyAtExit_Init(PyInterpreterState *interp);
+extern PyStatus _PyDateTime_InitTypes(PyInterpreterState *interp);
 
 /* Various internal finalizers */
 

@@ -7295,6 +7295,34 @@ def test_update_type_cache(self):
             """)
         script_helper.assert_python_ok('-c', script)
 
+    def test_concurrent_initialization_subinterpreter(self):
+        # gh-136421: Concurrent initialization of _datetime across multiple
+        # interpreters wasn't thread-safe due to its static types.
+
+        # Run in a subprocess to ensure we get a clean version of _datetime
+        script = """if True:
+        from concurrent.futures import InterpreterPoolExecutor
+
+        def func():
+            import _datetime
+            print('a', end='')
+
+        with InterpreterPoolExecutor() as executor:
+            for _ in range(8):
+                executor.submit(func)
+        """
+        rc, out, err = script_helper.assert_python_ok("-c", script)
+        self.assertEqual(rc, 0)
+        self.assertEqual(out, b"a" * 8)
+        self.assertEqual(err, b"")
+
+        # Now test against concurrent reinitialization
+        script = "import _datetime\n" + script
+        rc, out, err = script_helper.assert_python_ok("-c", script)
+        self.assertEqual(rc, 0)
+        self.assertEqual(out, b"a" * 8)
+        self.assertEqual(err, b"")
+
 
 def load_tests(loader, standard_tests, pattern):
     standard_tests.addTest(ZoneInfoCompleteTest())

diff --git a/Misc/NEWS.d/next/Core_and_Builtins/2025-07-12-09-59-14.gh-issue-136421.ZD1rNj.rst b/Misc/NEWS.d/next/Core_and_Builtins/2025-07-12-09-59-14.gh-issue-136421.ZD1rNj.rst
@@ -0,0 +1 @@
+Fix crash when initializing :mod:`datetime` concurrently.
@@ -12,6 +12,8 @@ posix posixmodule.c
 _signal signalmodule.c
 _tracemalloc _tracemalloc.c
 _suggestions _suggestions.c
+# needs libm and on some platforms librt
+_datetime _datetimemodule.c
 
 # modules used by importlib, deepfreeze, freeze, runpy, and sysconfig
 _codecs _codecsmodule.c

@@ -56,9 +56,6 @@
 @MODULE_CMATH_TRUE@cmath cmathmodule.c
 @MODULE__STATISTICS_TRUE@_statistics _statisticsmodule.c
 
-# needs libm and on some platforms librt
-@MODULE__DATETIME_TRUE@_datetime _datetimemodule.c
-
 # _decimal uses libmpdec
 # either static libmpdec.a from Modules/_decimal/libmpdec or libmpdec.so
 # with ./configure --with-system-libmpdec

@@ -14,6 +14,7 @@
 #include "pycore_object.h"        // _PyObject_Init()
 #include "pycore_time.h"          // _PyTime_ObjectToTime_t()
 #include "pycore_unicodeobject.h" // _PyUnicode_Copy()
+#include "pycore_initconfig.h"    // _PyStatus_OK()
 
 #include "datetime.h"
 
@@ -124,10 +125,9 @@ get_module_state(PyObject *module)
 #define INTERP_KEY ((PyObject *)&_Py_ID(cached_datetime_module))
 
 static PyObject *
-get_current_module(PyInterpreterState *interp, int *p_reloading)
+get_current_module(PyInterpreterState *interp)
 {
     PyObject *mod = NULL;
-    int reloading = 0;
 
     PyObject *dict = PyInterpreterState_GetDict(interp);
     if (dict == NULL) {
@@ -138,7 +138,6 @@ get_current_module(PyInterpreterState *interp, int *p_reloading)
         goto error;
     }
     if (ref != NULL) {
-        reloading = 1;
         if (ref != Py_None) {
             (void)PyWeakref_GetRef(ref, &mod);
             if (mod == Py_None) {
@@ -147,9 +146,6 @@ get_current_module(PyInterpreterState *interp, int *p_reloading)
             Py_DECREF(ref);
         }
     }
-    if (p_reloading != NULL) {
-        *p_reloading = reloading;
-    }
     return mod;
 
 error:
@@ -163,7 +159,7 @@ static datetime_state *
 _get_current_state(PyObject **p_mod)
 {
     PyInterpreterState *interp = PyInterpreterState_Get();
-    PyObject *mod = get_current_module(interp, NULL);
+    PyObject *mod = get_current_module(interp);
     if (mod == NULL) {
         assert(!PyErr_Occurred());
         if (PyErr_Occurred()) {
@@ -4482,7 +4478,7 @@ static PyTypeObject PyDateTime_TimeZoneType = {
     timezone_methods,                 /* tp_methods */
     0,                                /* tp_members */
     0,                                /* tp_getset */
-    0,                                /* tp_base; filled in PyInit__datetime */
+    &PyDateTime_TZInfoType,           /* tp_base */
     0,                                /* tp_dict */
     0,                                /* tp_descr_get */
     0,                                /* tp_descr_set */
@@ -7147,8 +7143,7 @@ static PyTypeObject PyDateTime_DateTimeType = {
     datetime_methods,                           /* tp_methods */
     0,                                          /* tp_members */
     datetime_getset,                            /* tp_getset */
-    0,                                          /* tp_base; filled in
-                                                   PyInit__datetime */
+    &PyDateTime_DateType,                       /* tp_base */
     0,                                          /* tp_dict */
     0,                                          /* tp_descr_get */
     0,                                          /* tp_descr_set */
@@ -7329,29 +7324,82 @@ clear_state(datetime_state *st)
 }
 
 
-static int
-init_static_types(PyInterpreterState *interp, int reloading)
+PyStatus
+_PyDateTime_InitTypes(PyInterpreterState *interp)
 {
-    if (reloading) {
-        return 0;
-    }
-
-    // `&...` is not a constant expression according to a strict reading
-    // of C standards. Fill tp_base at run-time rather than statically.
-    // See https://bugs.python.org/issue40777
-    PyDateTime_TimeZoneType.tp_base = &PyDateTime_TZInfoType;
-    PyDateTime_DateTimeType.tp_base = &PyDateTime_DateType;
-
     /* Bases classes must be initialized before subclasses,
      * so capi_types must have the types in the appropriate order. */
     for (size_t i = 0; i < Py_ARRAY_LENGTH(capi_types); i++) {
         PyTypeObject *type = capi_types[i];
         if (_PyStaticType_InitForExtension(interp, type) < 0) {
-            return -1;
+            return _PyStatus_ERR("could not initialize static types");
         }
     }
 
-    return 0;
+#define DATETIME_ADD_MACRO(dict, c, value_expr)         \
+    do {                                                \
+        assert(!PyErr_Occurred());                      \
+        PyObject *value = (value_expr);                 \
+        if (value == NULL) {                            \
+            goto error;                                 \
+        }                                               \
+        if (PyDict_SetItemString(dict, c, value) < 0) { \
+            Py_DECREF(value);                           \
+            goto error;                                 \
+        }                                               \
+        Py_DECREF(value);                               \
+    } while(0)
+
+    /* timedelta values */
+    PyObject *d = _PyType_GetDict(&PyDateTime_DeltaType);
+    DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
+    DATETIME_ADD_MACRO(d, "min", new_delta(-MAX_DELTA_DAYS, 0, 0, 0));
+    DATETIME_ADD_MACRO(d, "max",
+                        new_delta(MAX_DELTA_DAYS, 24*3600-1, 1000000-1, 0));
+
+    /* date values */
+    d = _PyType_GetDict(&PyDateTime_DateType);
+    DATETIME_ADD_MACRO(d, "min", new_date(1, 1, 1));
+    DATETIME_ADD_MACRO(d, "max", new_date(MAXYEAR, 12, 31));
+    DATETIME_ADD_MACRO(d, "resolution", new_delta(1, 0, 0, 0));
+
+    /* time values */
+    d = _PyType_GetDict(&PyDateTime_TimeType);
+    DATETIME_ADD_MACRO(d, "min", new_time(0, 0, 0, 0, Py_None, 0));
+    DATETIME_ADD_MACRO(d, "max", new_time(23, 59, 59, 999999, Py_None, 0));
+    DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
+
+    /* datetime values */
+    d = _PyType_GetDict(&PyDateTime_DateTimeType);
+    DATETIME_ADD_MACRO(d, "min",
+                        new_datetime(1, 1, 1, 0, 0, 0, 0, Py_None, 0));
+    DATETIME_ADD_MACRO(d, "max", new_datetime(MAXYEAR, 12, 31, 23, 59, 59,
+                                                999999, Py_None, 0));
+    DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
+
+    /* timezone values */
+    d = _PyType_GetDict(&PyDateTime_TimeZoneType);
+    if (PyDict_SetItemString(d, "utc", (PyObject *)&utc_timezone) < 0) {
+        goto error;
+    }
+
+    /* bpo-37642: These attributes are rounded to the nearest minute for backwards
+    * compatibility, even though the constructor will accept a wider range of
+    * values. This may change in the future.*/
+
+    /* -23:59 */
+    DATETIME_ADD_MACRO(d, "min", create_timezone_from_delta(-1, 60, 0, 1));
+
+    /* +23:59 */
+    DATETIME_ADD_MACRO(
+            d, "max", create_timezone_from_delta(0, (23 * 60 + 59) * 60, 0, 0));
+
+#undef DATETIME_ADD_MACRO
+
+    return _PyStatus_OK();
+
+error:
+    return _PyStatus_NO_MEMORY();
 }
 
 
@@ -7369,20 +7417,15 @@ _datetime_exec(PyObject *module)
 {
     int rc = -1;
     datetime_state *st = get_module_state(module);
-    int reloading = 0;
 
     PyInterpreterState *interp = PyInterpreterState_Get();
-    PyObject *old_module = get_current_module(interp, &reloading);
+    PyObject *old_module = get_current_module(interp);
     if (PyErr_Occurred()) {
         assert(old_module == NULL);
         goto error;
     }
     /* We actually set the "current" module right before a successful return. */
 
-    if (init_static_types(interp, reloading) < 0) {
-        goto error;
-    }
-
     for (size_t i = 0; i < Py_ARRAY_LENGTH(capi_types); i++) {
         PyTypeObject *type = capi_types[i];
         const char *name = _PyType_Name(type);
@@ -7396,68 +7439,6 @@ _datetime_exec(PyObject *module)
         goto error;
     }
 
-#define DATETIME_ADD_MACRO(dict, c, value_expr)         \
-    do {                                                \
-        assert(!PyErr_Occurred());                      \
-        PyObject *value = (value_expr);                 \
-        if (value == NULL) {                            \
-            goto error;                                 \
-        }                                               \
-        if (PyDict_SetItemString(dict, c, value) < 0) { \
-            Py_DECREF(value);                           \
-            goto error;                                 \
-        }                                               \
-        Py_DECREF(value);                               \
-    } while(0)
-
-    if (!reloading) {
-        /* timedelta values */
-        PyObject *d = _PyType_GetDict(&PyDateTime_DeltaType);
-        DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
-        DATETIME_ADD_MACRO(d, "min", new_delta(-MAX_DELTA_DAYS, 0, 0, 0));
-        DATETIME_ADD_MACRO(d, "max",
-                           new_delta(MAX_DELTA_DAYS, 24*3600-1, 1000000-1, 0));
-
-        /* date values */
-        d = _PyType_GetDict(&PyDateTime_DateType);
-        DATETIME_ADD_MACRO(d, "min", new_date(1, 1, 1));
-        DATETIME_ADD_MACRO(d, "max", new_date(MAXYEAR, 12, 31));
-        DATETIME_ADD_MACRO(d, "resolution", new_delta(1, 0, 0, 0));
-
-        /* time values */
-        d = _PyType_GetDict(&PyDateTime_TimeType);
-        DATETIME_ADD_MACRO(d, "min", new_time(0, 0, 0, 0, Py_None, 0));
-        DATETIME_ADD_MACRO(d, "max", new_time(23, 59, 59, 999999, Py_None, 0));
-        DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
-
-        /* datetime values */
-        d = _PyType_GetDict(&PyDateTime_DateTimeType);
-        DATETIME_ADD_MACRO(d, "min",
-                           new_datetime(1, 1, 1, 0, 0, 0, 0, Py_None, 0));
-        DATETIME_ADD_MACRO(d, "max", new_datetime(MAXYEAR, 12, 31, 23, 59, 59,
-                                                  999999, Py_None, 0));
-        DATETIME_ADD_MACRO(d, "resolution", new_delta(0, 0, 1, 0));
-
-        /* timezone values */
-        d = _PyType_GetDict(&PyDateTime_TimeZoneType);
-        if (PyDict_SetItemString(d, "utc", (PyObject *)&utc_timezone) < 0) {
-            goto error;
-        }
-
-        /* bpo-37642: These attributes are rounded to the nearest minute for backwards
-        * compatibility, even though the constructor will accept a wider range of
-        * values. This may change in the future.*/
-
-        /* -23:59 */
-        DATETIME_ADD_MACRO(d, "min", create_timezone_from_delta(-1, 60, 0, 1));
-
-        /* +23:59 */
-        DATETIME_ADD_MACRO(
-                d, "max", create_timezone_from_delta(0, (23 * 60 + 59) * 60, 0, 0));
-    }
-
-#undef DATETIME_ADD_MACRO
-
     /* Add module level attributes */
     if (PyModule_AddIntMacro(module, MINYEAR) < 0) {
         goto error;

@@ -106,6 +106,7 @@
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\Modules\atexitmodule.c" />
+    <ClCompile Include="..\Modules\_datetimemodule.c" />
     <ClCompile Include="..\Modules\faulthandler.c" />
     <ClCompile Include="..\Modules\gcmodule.c" />
     <ClCompile Include="..\Modules\getbuildinfo.c" />

@@ -760,6 +760,11 @@ pycore_init_types(PyInterpreterState *interp)
         return status;
     }
 
+    status = _PyDateTime_InitTypes(interp);
+    if (_PyStatus_EXCEPTION(status)) {
+        return status;
+    }
-    status = _PyDateTime_InitTypes(interp);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    if (!_Py_IsMainInterpreter(interp)) {
+        status = _PyDateTime_InitTypes(interp);
+        if (_PyStatus_EXCEPTION(status)) {
+            return status;
+        }
+    }
-    status = _PyDateTime_InitTypes(interp);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    if (!_Py_IsMainInterpreter(interp)) {
+        status = _PyDateTime_InitTypes(interp);
+        if (_PyStatus_EXCEPTION(status)) {
+            return status;
+        }
+    }
+
     return _PyStatus_OK();
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix crash when initializing :mod:`datetime` concurrently.