From 7adbb5a35da601fc68255eeaf341ad734e86a9bf Mon Sep 17 00:00:00 2001
From: Benjamin Peterson <benjamin@python.org>
Date: Sat, 3 Oct 2009 20:23:24 +0000
Subject: [PATCH] #7050 fix a SystemError when using tuple unpacking and
 augmented assignment

---
 Lib/test/test_augassign.py |  3 +++
 Misc/NEWS                  |  3 +++
 Python/ast.c               | 13 +++++++++++++
 3 files changed, 19 insertions(+)

diff --git a/Lib/test/test_augassign.py b/Lib/test/test_augassign.py
index 24aa2b7c9e3..a5b7cc4aaa0 100644
--- a/Lib/test/test_augassign.py
+++ b/Lib/test/test_augassign.py
@@ -24,6 +24,9 @@ class AugAssignTest(unittest.TestCase):
             # new-style division (with -Qnew)
             self.assertEquals(x, 3.0)
 
+    def test_with_unpacking(self):
+        self.assertRaises(SyntaxError, compile, "x, b += 3", "<test>", "exec")
+
     def testInList(self):
         x = [2]
         x[0] += 1
diff --git a/Misc/NEWS b/Misc/NEWS
index dc54329db9a..bafb0ab5d15 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@ What's New in Python 2.7 alpha 1
 Core and Builtins
 -----------------
 
+- Issue #7050: Fix a SystemError when trying to use unpacking and augmented
+  assignment.
+
 - Issue #5329: Fix os.popen* regression from 2.5 with commands as a
   sequence running through the shell.  Patch by Jean-Paul Calderone
   and Jani Hakala.
diff --git a/Python/ast.c b/Python/ast.c
index 2f975ac8e0a..3422c2e1b0d 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -2097,6 +2097,19 @@ ast_for_expr_stmt(struct compiling *c, const node *n)
             return NULL;
         if(!set_context(c, expr1, Store, ch))
             return NULL;
+        /* set_context checks that most expressions are not the left side.
+          Augmented assignments can only have a name, a subscript, or an
+          attribute on the left, though, so we have to explicitly check for
+          those. */
+        switch (expr1->kind) {
+            case Name_kind:
+            case Attribute_kind:
+            case Subscript_kind:
+                break;
+            default:
+                ast_error(ch, "illegal expression for augmented assignment");
+                return NULL;
+        }
 
         ch = CHILD(n, 2);
         if (TYPE(ch) == testlist)