WIP

Grammar/Tokens

@@ -54,6 +54,7 @@ RARROW                  '->'
 ELLIPSIS                '...'
 COLONEQUAL              ':='
 EXCLAMATION             '!'
+QUESTIONMARKDOT         '?.'
 
 OP
 TYPE_IGNORE

Grammar/python.gram

@@ -545,6 +545,10 @@ attr[expr_ty]:
     | value=name_or_attr '.' attr=NAME {
         _PyAST_Attribute(value, attr->v.Name.id, Load, EXTRA) }
 
+safe_attr[expr_ty]:
+    | value=name_or_attr '.' attr=NAME {
+        _PyAST_SafeAttribute(value, attr->v.Name.id, Load, EXTRA) }
+
 name_or_attr[expr_ty]:
     | attr
     | NAME
@@ -822,6 +826,7 @@ await_primary[expr_ty] (memo):
 
 primary[expr_ty]:
     | a=primary '.' b=NAME { _PyAST_Attribute(a, b->v.Name.id, Load, EXTRA) }
+    | a=primary '?.' b=NAME { _PyAST_SafeAttribute(a, b->v.Name.id, Load, EXTRA) }
     | a=primary b=genexp { _PyAST_Call(a, CHECK(asdl_expr_seq*, (asdl_expr_seq*)_PyPegen_singleton_seq(p, b)), NULL, EXTRA) }
     | a=primary '(' b=[arguments] ')' {
         _PyAST_Call(a,

Include/internal/pycore_token.h

@@ -68,17 +68,18 @@ extern "C" {
 #define ELLIPSIS        52
 #define COLONEQUAL      53
 #define EXCLAMATION     54
-#define OP              55
-#define TYPE_IGNORE     56
-#define TYPE_COMMENT    57
-#define SOFT_KEYWORD    58
-#define FSTRING_START   59
-#define FSTRING_MIDDLE  60
-#define FSTRING_END     61
-#define COMMENT         62
-#define NL              63
-#define ERRORTOKEN      64
-#define N_TOKENS        66
+#define QUESTIONMARKDOT 55
+#define OP              56
+#define TYPE_IGNORE     57
+#define TYPE_COMMENT    58
+#define SOFT_KEYWORD    59
+#define FSTRING_START   60
+#define FSTRING_MIDDLE  61
+#define FSTRING_END     62
+#define COMMENT         63
+#define NL              64
+#define ERRORTOKEN      65
+#define N_TOKENS        67
 #define NT_OFFSET       256
 
 /* Special definitions for cooperation with parser */

Lib/test/test_safeattr.py

@@ -0,0 +1,46 @@
+import unittest
+from Lib.test.test_syntax import SyntaxTestCase
+
+
+class A:
+    def __init__(self) -> None:
+        self.b = 0
+
+
+class SafeAttrTest(SyntaxTestCase):
+    def test_safe_attr_is_safe(self):
+        a = None
+        with self.assertRaises(AttributeError):
+            a.b
+        assert a?.b is None
+
+    def test_safe_attr_nonnull_case(self):
+        a = A()
+        assert a.b == a?.b == 0
+
+    def test_cannot_delete_with_safe_attr(self):
+        self._check_error("""
+class A:
+    def __init__(self) -> None:
+        self.b = 0
+a = A()
+
+del a.b
+
+del a?.b
+""", "syntax")
+
+
+    def test_cannot_store_with_safe_attr(self):
+        self._check_error("""
+class A:
+    def __init__(self) -> None:
+        self.b = 0
+a = A()
+a.b = 4
+a?.b = 3
+""", "cannot assign to safe attribute here")
+
+
+if __name__ == '__main__':
+    unittest.main()

Lib/test/test_until.py

@@ -9,5 +9,3 @@ def test_until(self):
 
 if __name__ == '__main__':
     unittest.main()
-
-

Parser/Python.asdl

@@ -84,6 +84,7 @@ module Python
 
          -- the following expression can appear in assignment context
          | Attribute(expr value, identifier attr, expr_context ctx)
+         | SafeAttribute(expr value, identifier attr, expr_context ctx)
          | Subscript(expr value, expr slice, expr_context ctx)
          | Starred(expr value, expr_context ctx)
          | Name(identifier id, expr_context ctx)

Parser/action_helpers.c

@@ -323,6 +323,15 @@ _set_attribute_context(Parser *p, expr_ty e, expr_context_ty ctx)
                             ctx, EXTRA_EXPR(e, e));
 }
 
+
+static expr_ty
+_set_safe_attribute_context(Parser *p, expr_ty e, expr_context_ty ctx)
+{
+    return _PyAST_SafeAttribute(e->v.SafeAttribute.value, e->v.SafeAttribute.attr,
+                                ctx, EXTRA_EXPR(e, e));
+}
+
+
 static expr_ty
 _set_starred_context(Parser *p, expr_ty e, expr_context_ty ctx)
 {
@@ -353,6 +362,9 @@ _PyPegen_set_expr_context(Parser *p, expr_ty expr, expr_context_ty ctx)
         case Attribute_kind:
             new = _set_attribute_context(p, expr, ctx);
             break;
+        case SafeAttribute_kind:
+            new = _set_safe_attribute_context(p, expr, ctx);
+            break;
         case Starred_kind:
             new = _set_starred_context(p, expr, ctx);
             break;
@@ -1042,6 +1054,8 @@ _PyPegen_get_expr_name(expr_ty e)
     switch (e->kind) {
         case Attribute_kind:
             return "attribute";
+        case SafeAttribute_kind:
+            return "safe attribute";
         case Subscript_kind:
             return "subscript";
         case Starred_kind:
@@ -1204,6 +1218,7 @@ _PyPegen_get_invalid_target(expr_ty e, TARGETS_TYPE targets_type)
         case Name_kind:
         case Subscript_kind:
         case Attribute_kind:
+        case SafeAttribute_kind:
             return NULL;
         default:
             return e;