May 10, 2025 · May 10, 2025 · May 10, 2025 · May 10, 2025 · May 10, 2025
diff --git a/Lib/test/test_ast/test_ast.py b/Lib/test/test_ast/test_ast.py
 self.assertIs(repl.id,'y')
 self.assertIs(repl.ctx,context)

 deftest_replace_accept_missing_field_with_default(self):
 node=ast.FunctionDef(name="foo",args=ast.arguments())
 self.assertIs(node.returns,None)
 self.assertEqual(node.decorator_list, [])
 node2=copy.replace(node,name="bar")
 self.assertEqual(node2.name,"bar")
 self.assertIs(node2.returns,None)
 self.assertEqual(node2.decorator_list, [])

 deftest_replace_reject_known_custom_instance_fields_commits(self):
 node=ast.parse('x').body[0].value
 node.extra=extra=object()# add instance 'extra' field
diff --git a/Misc/NEWS.d/next/Library/2025-05-09-19-05-24.gh-issue-133783.1voCnR.rst b/Misc/NEWS.d/next/Library/2025-05-09-19-05-24.gh-issue-133783.1voCnR.rst
 Fix bug with applying:func:`copy.replace` to:mod:`ast` objects. Attributes
 that default to ``None`` were incorrectly treated as required for manually
 created AST nodes.
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
            Py_DECREF(unused);
        }
    }

    // Discard fields from 'expecting' that default to None
    PyObject *field_types = NULL;
    if (PyObject_GetOptionalAttr((PyObject*)Py_TYPE(self),
                                 &_Py_ID(_field_types),
                                 &field_types) < 0)
    {
        Py_DECREF(expecting);
        return -1;
    }
    if (field_types != NULL) {
        Py_ssize_t pos = 0;
        PyObject *field_name, *field_type;
        while (PyDict_Next(field_types, &pos, &field_name, &field_type)) {
            if (_PyUnion_Check(field_type)) {
                // optional field
                if (PySet_Discard(expecting, field_name) < 0) {
                    Py_DECREF(expecting);
                    Py_DECREF(field_types);
                    return -1;
                }
            }
        }
        Py_DECREF(field_types);
    }

    // Now 'expecting' contains the fields or attributes
    // that would not be filled inside ast_type_replace().
    Py_ssize_t m = PySet_GET_SIZE(expecting);
diff --git a/Python/Python-ast.c b/Python/Python-ast.c
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1315,6 +1315,15 @@ def test_replace_reject_missing_field(self):
		self.assertIs(repl.id,'y')
		self.assertIs(repl.ctx,context)

		deftest_replace_accept_missing_field_with_default(self):
		node=ast.FunctionDef(name="foo",args=ast.arguments())
		self.assertIs(node.returns,None)
		self.assertEqual(node.decorator_list, [])
		node2=copy.replace(node,name="bar")
		self.assertEqual(node2.name,"bar")
		self.assertIs(node2.returns,None)
		self.assertEqual(node2.decorator_list, [])

		deftest_replace_reject_known_custom_instance_fields_commits(self):
		node=ast.parse('x').body[0].value
		node.extra=extra=object()# add instance 'extra' field
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Fix bug with applying:func:`copy.replace` to:mod:`ast` objects. Attributes
		that default to ``None`` were incorrectly treated as required for manually
		created AST nodes.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1244,6 +1244,32 @@ def visitModule(self, mod):
		Py_DECREF(unused);
		}
		}

		// Discard fields from 'expecting' that default to None
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		PyObject *field_types = NULL;
		if (PyObject_GetOptionalAttr((PyObject*)Py_TYPE(self),
		&_Py_ID(_field_types),
		&field_types) < 0)
		{
		Py_DECREF(expecting);
		return -1;
		}
		if (field_types != NULL) {
		Py_ssize_t pos = 0;
		PyObject field_name, field_type;
		while (PyDict_Next(field_types, &pos, &field_name, &field_type)) {
		if (_PyUnion_Check(field_type)) {
		// optional field
		if (PySet_Discard(expecting, field_name) < 0) {
		Py_DECREF(expecting);
		Py_DECREF(field_types);
		return -1;
		}
		}
		}
		Py_DECREF(field_types);
		}

		// Now 'expecting' contains the fields or attributes
		// that would not be filled inside ast_type_replace().
		Py_ssize_t m = PySet_GET_SIZE(expecting);
Expand Down