prevent assignment to set literals

Lib/test/test_syntax.py

@@ -468,6 +468,12 @@ Traceback (most recent call last):
   File "<doctest test.test_syntax[50]>", line 1
 SyntaxError: can't delete ()
 
+>>> {1, 2, 3} = 42
+Traceback (most recent call last):
+   ...
+   File "<doctest test.test_syntax[50]>", line 1
+SyntaxError: can't assign to literal
+
 """
 
 import re

Misc/NEWS

@@ -12,6 +12,8 @@ What's New in Python 2.7?
 Core and Builtins
 -----------------
 
+- Prevent assignment to set literals.
+
 Library
 -------
 

Python/ast.c

@@ -440,6 +440,7 @@ set_context(struct compiling *c, expr_ty e, expr_context_ty ctx, const node *n)
             expr_name = "dict comprehension";
             break;
         case Dict_kind:
+        case Set_kind:
         case Num_kind:
         case Str_kind:
             expr_name = "literal";