gh-148058: Do not refleak when XMLParser.__init__() called many times

Lib/test/test_xml_etree_c.py

@@ -1,6 +1,7 @@
 # xml.etree test for cElementTree
 import io
 import struct
+import sys
 from test import support
 from test.support.import_helper import import_fresh_module
 import types
@@ -171,6 +172,20 @@ def test_xmlpullparser_leaks(self):
         del parser
         support.gc_collect()
 
+    @support.refcount_test
+    def test_xmlparser_refleaks_in___init__(self):
+        gettotalrefcount = support.get_attribute(sys, 'gettotalrefcount')
+        parser = cET.XMLParser()
+        lastrc = gettotalrefcount()
+        for i in range(20):
+            support.gc_collect()
+            rc = gettotalrefcount()
+            for _ in range(100):
+                parser.__init__()
+            delta = rc - lastrc
+            lastrc = rc
+        self.assertLess(delta, 3)
+
     def test_dict_disappearing_during_get_item(self):
         # test fix for seg fault reported in issue 27946
         class X:

Misc/NEWS.d/next/Library/2026-04-04-00-37-39.gh-issue-148058.zMIVaS.rst

@@ -0,0 +1,3 @@
+Fix reference leak in :class:`xml.etree.ElementTree.XMLParser` when
+:meth:`~object.__init__` is called many times. Patch by Maurycy
+Pawłowski-Wieroński.

Modules/_elementtree.c

@@ -3699,6 +3699,8 @@ ignore_attribute_error(PyObject *value)
     return 0;
 }
 
+static int xmlparser_gc_clear(PyObject *op);
+
 /*[clinic input]
 _elementtree.XMLParser.__init__
 
@@ -3713,6 +3715,10 @@ _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *target,
                                      const char *encoding)
 /*[clinic end generated code: output=3ae45ec6cdf344e4 input=7e716dd6e4f3e439]*/
 {
+    if (self->parser != NULL) {
+        (void)xmlparser_gc_clear((PyObject *)self);
+    }
+
     self->entity = PyDict_New();
     if (!self->entity)
         return -1;