bpo-45948: Remove constructor discrepancy in C version of ElementTree.XMLParser

Lib/test/test_xml_etree.py

@@ -758,6 +758,15 @@ def end_ns(self, prefix):
                 ('end-ns', ''),
             ])
 
+    def test_initialize_parser_without_target(self):
+        # Explicit None
+        parser = ET.XMLParser(target=None)
+        self.assertIsInstance(parser.target, ET.TreeBuilder)
+
+        # Implicit None
+        parser2 = ET.XMLParser()
+        self.assertIsInstance(parser2.target, ET.TreeBuilder)
+
     def test_children(self):
         # Test Element children iteration
 

Misc/NEWS.d/next/Library/2022-02-05-18-22-05.bpo-45948.w4mCnE.rst

@@ -0,0 +1,5 @@
+Fixed a discrepancy in the C implementation of the
+:mod:`xml.etree.ElementTree` module. Now, instantiating an
+:class:`xml.etree.ElementTree.XMLParser` with a ``target=None``
+keyword provides a default :class:`xml.etree.ElementTree.TreeBuilder`
+target as the Python implementation does.

Modules/_elementtree.c

@@ -3636,15 +3636,15 @@ ignore_attribute_error(PyObject *value)
 _elementtree.XMLParser.__init__
 
     *
-    target: object = NULL
+    target: object = None
     encoding: str(accept={str, NoneType}) = None
 
 [clinic start generated code]*/
 
 static int
 _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *target,
                                      const char *encoding)
-/*[clinic end generated code: output=3ae45ec6cdf344e4 input=53e35a829ae043e8]*/
+/*[clinic end generated code: output=3ae45ec6cdf344e4 input=7e716dd6e4f3e439]*/
 {
     self->entity = PyDict_New();
     if (!self->entity)
@@ -3669,7 +3669,7 @@ _elementtree_XMLParser___init___impl(XMLParserObject *self, PyObject *target,
                            (unsigned long)_Py_HashSecret.expat.hashsalt);
     }
 
-    if (target) {
+    if (target != Py_None) {
         Py_INCREF(target);
     } else {
         target = treebuilder_new(&TreeBuilder_Type, NULL, NULL);