Update Grammar/python.gram

Co-authored-by: Lysandros Nikolaou <lisandrosnik@gmail.com>

Author: pablogsal

Grammar/python.gram

@@ -640,11 +640,21 @@ invalid_assignment:
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "only single target (not tuple) can be annotated") }
     | a=expression ':' expression ['=' annotated_rhs] {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION(a, "illegal target for annotation") }
-    | a=expression ('=' | augassign) (yield_expr | star_expressions) {
+    | a=star_expressions '=' (yield_expr | star_expressions) {
         RAISE_SYNTAX_ERROR_KNOWN_LOCATION( 
             _PyPegen_get_invalid_target(a), 
             "cannot assign to %s", _PyPegen_get_expr_name(_PyPegen_get_invalid_target(a))
         )}
+    | a=expression augassign (yield_expr | star_expressions) {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION( 
+            _PyPegen_get_invalid_target(a), 
+            "cannot assign to %s", _PyPegen_get_expr_name(_PyPegen_get_invalid_target(a))
+        )}
+    | a=star_expressions augassign (yield_expr | star_expressions) {
+        RAISE_SYNTAX_ERROR_KNOWN_LOCATION( 
+            a, 
+            "illegal expression for augmented assignment"
+        )}
 invalid_block:
     | NEWLINE !INDENT { RAISE_INDENTATION_ERROR("expected an indented block") }
 invalid_comprehension:

Lib/test/test_foo.py

@@ -124,6 +124,14 @@
 Traceback (most recent call last):
 SyntaxError: cannot assign to operator
 
+>>> [a, b[1], c + 1] = [1, 2, 3]
+Traceback (most recent call last):
+SyntaxError: cannot assign to operator
+
+>>> [a, b.c.d, c + 1] = [1, 2, 3]
+Traceback (most recent call last):
+SyntaxError: cannot assign to operator
+
 >>> a if 1 else b = 1
 Traceback (most recent call last):
 SyntaxError: cannot assign to conditional expression