Very subtle syntax change: in a list comprehension, the testlist in

"for <var> in <testlist> may no longer be a single test followed by
a comma.  This solves SF bug #431886.  Note that if the testlist
contains more than one test, a trailing comma is still allowed, for
maximum backward compatibility; but this example is not:

    [(x, y) for x in range(10), for y in range(10)]
                              ^

The fix involved creating a new nonterminal 'testlist_safe' whose
definition doesn't allow the trailing comma if there's only one test:

    testlist_safe: test [(',' test)+ [',']]

1 files changed, 9 insertions, 1 deletions

diff --git a/Modules/parsermodule.c b/Modules/parsermodule.c
index bc82ce5..000e639 100644
--- a/Modules/parsermodule.c
+++ b/Modules/parsermodule.c
@@ -1039,6 +1039,14 @@ validate_testlist(node *tree)
 }
 
 
+static int
+validate_testlist_safe(node *tree)
+{
+    return (validate_repeating_list(tree, testlist_safe,
+                                    validate_test, "testlist_safe"));
+}
+
+
 /* '*' NAME [',' '**' NAME] | '**' NAME
  */
 static int
@@ -1218,7 +1226,7 @@ validate_list_for(node *tree)
         res = (validate_name(CHILD(tree, 0), "for")
                && validate_exprlist(CHILD(tree, 1))
                && validate_name(CHILD(tree, 2), "in")
-               && validate_testlist(CHILD(tree, 3)));
+               && validate_testlist_safe(CHILD(tree, 3)));
 
     return res;
 }