python · gourijain029-del · Feb 25, 2026 · Feb 26, 2026
@@ -79,7 +79,10 @@ def _Popen(self):
 
     def __init__(self, group=None, target=None, name=None, args=(), kwargs=None,
                  *, daemon=None):
-        assert group is None, 'group argument must be None for now'
+        if group is not None:
+            raise TypeError("group argument must be None for now")
+        if target is not None and not callable(target):
+            raise TypeError("target must be callable")
         count = next(_process_counter)
         self._identity = _current_process._identity + (count,)
         self._config = _current_process._config.copy()

@@ -326,6 +326,12 @@ def test_current(self):
         self.assertEqual(current.ident, os.getpid())
         self.assertEqual(current.exitcode, None)
 
+    def test_invalid_args(self):
+        with self.assertRaisesRegex(TypeError, "group argument must be None"):
+            self.Process(group="not None")
+        with self.assertRaisesRegex(TypeError, "target must be callable"):
+            self.Process(target=123)
+
     @warnings_helper.ignore_fork_in_thread_deprecation_warnings()
     def test_set_executable(self):
         if self.TYPE == 'threads':

diff --git a/Lib/test/test_threading.py b/Lib/test/test_threading.py
@@ -151,6 +151,12 @@ def func(): pass
             thread = threading.Thread(target=func)
             self.assertEqual(thread.name, "Thread-5 (func)")
 
+    def test_invalid_args(self):
+        with self.assertRaisesRegex(TypeError, "group argument must be None"):
+            threading.Thread(group="not None")
+        with self.assertRaisesRegex(TypeError, "target must be callable"):
+            threading.Thread(target=123)
+
     def test_args_argument(self):
         # bpo-45735: Using list or tuple as *args* in constructor could
         # achieve the same effect.

diff --git a/Lib/threading.py b/Lib/threading.py
@@ -901,7 +901,10 @@ class is implemented.
         else to the thread.
 
         """
-        assert group is None, "group argument must be None for now"
+        if group is not None:
+            raise TypeError("group argument must be None for now")
+        if target is not None and not callable(target):
+            raise TypeError("target must be callable")
         if kwargs is None:
             kwargs = {}
         if name:

diff --git a/Misc/NEWS.d/next/Library/2026-02-25-14-30-00.gh-issue-145202.xR3f9A.rst b/Misc/NEWS.d/next/Library/2026-02-25-14-30-00.gh-issue-145202.xR3f9A.rst
@@ -0,0 +1 @@
+Fix a segmentation fault in :func:`unicodedata.iter_graphemes` when the iterator is deallocated after being cleared by the garbage collector.
diff --git a/Misc/NEWS.d/next/Library/2026-02-26-09-30-00.gh-issue-145242.N7hA6L.rst b/Misc/NEWS.d/next/Library/2026-02-26-09-30-00.gh-issue-145242.N7hA6L.rst
@@ -0,0 +1 @@
+Added early validation of the ``target`` argument in :class:`threading.Thread` and :class:`multiprocessing.Process` constructors. If ``target`` is not callable, a :exc:`TypeError` is now raised immediately in the calling thread, resulting in a clearer traceback. Optimized the validation of the reserved ``group`` argument by replacing internal assertions with :exc:`TypeError`.
diff --git a/Modules/unicodedata.c b/Modules/unicodedata.c
@@ -1913,7 +1913,7 @@ Segment_dealloc(PyObject *self)
 {
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
-    Py_DECREF(((SegmentObject *)self)->string);
+    Py_XDECREF(((SegmentObject *)self)->string);
     tp->tp_free(self);
     Py_DECREF(tp);
 }
@@ -1989,7 +1989,7 @@ GBI_dealloc(PyObject *self)
 {
     PyTypeObject *tp = Py_TYPE(self);
     PyObject_GC_UnTrack(self);
-    Py_DECREF(((GraphemeBreakIterator *)self)->iter.str);
+    Py_XDECREF(((GraphemeBreakIterator *)self)->iter.str);
     tp->tp_free(self);
     Py_DECREF(tp);
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Fix a segmentation fault in :func:`unicodedata.iter_graphemes` when the iterator is deallocated after being cleared by the garbage collector.
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1 @@
		Added early validation of the ``target`` argument in :class:`threading.Thread` and :class:`multiprocessing.Process` constructors. If ``target`` is not callable, a :exc:`TypeError` is now raised immediately in the calling thread, resulting in a clearer traceback. Optimized the validation of the reserved ``group`` argument by replacing internal assertions with :exc:`TypeError`.