gh-153537: Fix Element re-init memory leak in the C accelerator

element_init allocated a new extra without releasing the previous one,
leaking the element's children and attributes on a second __init__ call.
Clear the old extra first, so re-init discards the previous children and
attributes, matching the pure-Python implementation.

Author: tonghuaroot

Lib/test/test_xml_etree.py

@@ -2654,6 +2654,19 @@ def f():
 
 class BasicElementTest(ElementTestCase, unittest.TestCase):
 
+    def test_reinit_releases_children(self):
+        # gh-153537: re-init should release the previous children.
+        e = ET.Element('a', {'k': 'v'})
+        children = [ET.SubElement(e, 'b') for _ in range(3)]
+        refs = [weakref.ref(c) for c in children]
+        del children
+        self.assertEqual(len(e), 3)
+        e.__init__('a')
+        gc_collect()
+        self.assertEqual(len(e), 0)
+        self.assertEqual(e.attrib, {})
+        self.assertTrue(all(ref() is None for ref in refs))
+
     def test___init__(self):
         tag = "foo"
         attrib = { "zix": "wyp" }

Misc/NEWS.d/next/Library/2026-07-11-11-36-15.gh-issue-153537.2KySPQ.rst

@@ -0,0 +1,3 @@
+Re-initializing an :class:`xml.etree.ElementTree.Element` in the C accelerator
+now discards the previous children and attributes instead of leaking them,
+matching the pure-Python implementation. Patch by tonghuaroot.

Modules/_elementtree.c

@@ -449,6 +449,9 @@ element_init(PyObject *self, PyObject *args, PyObject *kwds)
 
     self_elem = (ElementObject *)self;
 
+    /* On re-init, drop any children and attrib from a previous init. */
+    clear_extra(self_elem);
+
     if (attrib != NULL && !is_empty_dict(attrib)) {
         if (create_extra(self_elem, attrib) < 0) {
             Py_DECREF(attrib);