Issue #13343: Fix a SystemError when a lambda expression uses a global

variable in the default value of a keyword-only argument:
(lambda *, arg=GLOBAL_NAME: None)

Lib/test/test_keywordonlyarg.py

@@ -162,6 +162,14 @@ class KeywordOnlyArgTestCase(unittest.TestCase):
         self.assertEqual(Example.f(Example(), k1=1, k2=2), (1, 2))
         self.assertRaises(TypeError, Example.f, k1=1, k2=2)
 
+    def test_issue13343(self):
+        # The Python compiler must scan all symbols of a function to
+        # determine their scope: global, local, cell...
+        # This was not done for the default values of keyword
+        # arguments in a lambda definition, and the following line
+        # used to fail with a SystemError.
+        lambda *, k1=unittest: None
+
 def test_main():
     run_unittest(KeywordOnlyArgTestCase)
 

Misc/NEWS

@@ -10,6 +10,10 @@ What's New in Python 3.3 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #13343: Fix a SystemError when a lambda expression uses a global
+  variable in the default value of a keyword-only argument:
+  (lambda *, arg=GLOBAL_NAME: None)
+
 - Issue #12797: Added custom opener parameter to builtin open() and
   FileIO.open().
 

Python/symtable.c

@@ -1300,6 +1300,9 @@ symtable_visit_expr(struct symtable *st, expr_ty e)
             return 0;
         if (e->v.Lambda.args->defaults)
             VISIT_SEQ(st, expr, e->v.Lambda.args->defaults);
+        if (e->v.Lambda.args->kw_defaults)
+            VISIT_KWONLYDEFAULTS(st,
+                                 e->v.Lambda.args->kw_defaults);
         if (!symtable_enter_block(st, lambda,
                                   FunctionBlock, (void *)e, e->lineno,
                                   e->col_offset))