docs

Doc/library/ast.rst

@@ -103,20 +103,15 @@ Node classes
    For example, to create and populate an :class:`ast.UnaryOp` node, you could
    use ::
 
-      node = ast.UnaryOp()
-      node.op = ast.USub()
-      node.operand = ast.Constant()
-      node.operand.value = 5
-      node.operand.lineno = 0
-      node.operand.col_offset = 0
-      node.lineno = 0
-      node.col_offset = 0
-
-   or the more compact ::
-
       node = ast.UnaryOp(ast.USub(), ast.Constant(5, lineno=0, col_offset=0),
                          lineno=0, col_offset=0)
 
+   If a field that is optional in the grammar is omitted from the constructor,
+   it defaults to ``None``. If a list field is omitted, it defaults to the empty
+   list. If any other field is omitted, a :exc:`DeprecationWarning` is raised
+   and the AST node will not have this field. In Python 3.15, this condition will
+   raise an error.
+
 .. versionchanged:: 3.8
 
    Class :class:`ast.Constant` is now used for all constants.
@@ -140,6 +135,14 @@ Node classes
    In the meantime, instantiating them will return an instance of
    a different class.
 
+.. deprecated:: 3.13
+
+   Previous versions of Python allowed the creation of AST nodes missing
+   required fields. Similarly, AST node constructors allowed arbitrary keyword
+   arguments that were set as attributes of the AST node, even if they didd not
+   match any of the fields of the AST node. This behavior is deprecated and will
+   be removed in Python 3.15.
+
 .. note::
     The descriptions of the specific node classes displayed here
     were initially adapted from the fantastic `Green Tree

Doc/whatsnew/3.13.rst

@@ -206,6 +206,14 @@ array
 ast
 ---
 
+* The constructors of node types in the :mod:`ast` module are stricter
+  in the arguments they accept. If an optional field is not passed to the
+  constructor, it is set to ``None``, and if a list field is not passed,
+  it is set to the empty list. (Previously, the attribute would be missing.)
+  If any other field is not passed to the constructor, a :exc:`DeprecationWarning`
+  is raised. This will raise an exception in Python 3.15. Similarly, passing
+  a keyword argument that does not map to a field on the AST node now raises
+  a :exc:`DeprecationWarning` and will raise an exception in Python 3.15.
 * :func:`ast.parse` now accepts an optional argument ``optimize``
   which is passed on to the :func:`compile` built-in. This makes it
   possible to obtain an optimized ``AST``.