https://github.com/python/cpython/commit/7dddb4e667b5eb76cbe11755051ec139b0f437a9
commit: 7dddb4e667b5eb76cbe11755051ec139b0f437a9
branch: main
author: Jelle Zijlstra <jelle.zijls...@gmail.com>
committer: JelleZijlstra <jelle.zijls...@gmail.com>
date: 2025-05-10T09:17:38-07:00
summary:
gh-133783: Fix __replace__ on AST nodes for optional attributes (#133797)
files:
A Misc/NEWS.d/next/Library/2025-05-09-19-05-24.gh-issue-133783.1voCnR.rst
M Lib/test/test_ast/test_ast.py
M Parser/asdl_c.py
M Python/Python-ast.c
diff --git a/Lib/test/test_ast/test_ast.py b/Lib/test/test_ast/test_ast.py
index 02628868db008c..0776559b9003db 100644
--- a/Lib/test/test_ast/test_ast.py
+++ b/Lib/test/test_ast/test_ast.py
@@ -1315,6 +1315,15 @@ def test_replace_reject_missing_field(self):
self.assertIs(repl.id, 'y')
self.assertIs(repl.ctx, context)
+ def test_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, [])
+
def test_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
new file mode 100644
index 00000000000000..62e742df17954e
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-05-09-19-05-24.gh-issue-133783.1voCnR.rst
@@ -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.
diff --git a/Parser/asdl_c.py b/Parser/asdl_c.py
index 09e014534fbabc..22dcfe1b0d99bf 100755
--- a/Parser/asdl_c.py
+++ b/Parser/asdl_c.py
@@ -1244,6 +1244,32 @@ def visitModule(self, mod):
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
index df035568f84be1..f7625ab1205bdc 100644
--- a/Python/Python-ast.c
+++ b/Python/Python-ast.c
@@ -5528,6 +5528,32 @@ ast_type_replace_check(PyObject *self,
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);
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