correctly overflow when indexes are too large

Lib/test/test_unicode.py

@@ -1282,6 +1282,9 @@ class UnicodeTest(
         self.assertRaises(IndexError, u"{:}".format)
         self.assertRaises(IndexError, u"{:s}".format)
         self.assertRaises(IndexError, u"{}".format)
+        big = "23098475029384702983476098230754973209482573"
+        self.assertRaises(ValueError, ("{" + big + "}").format)
+        self.assertRaises(ValueError, ("{[" + big + "]}").format, [0])
 
         # issue 6089
         self.assertRaises(ValueError, u"{0[0]x}".format, [None])

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python release candidate 2?
 Core and Builtins
 -----------------
 
+- In the unicode/str.format(), raise a ValueError when either indexes to
+  arguments are too large.
+
 Library
 -------
 

Objects/stringlib/string_format.h

@@ -373,6 +373,8 @@ FieldNameIterator_next(FieldNameIterator *self, int *is_attribute,
         if (_FieldNameIterator_item(self, name) == 0)
             return 0;
         *name_idx = get_integer(name);
+        if (*name_idx == -1 && PyErr_Occurred())
+            return 0;
         break;
     default:
         /* Invalid character follows ']' */
@@ -429,6 +431,8 @@ field_name_split(STRINGLIB_CHAR *ptr, Py_ssize_t len, SubString *first,
 
     /* see if "first" is an integer, in which case it's used as an index */
     *first_idx = get_integer(first);
+    if (*first_idx == -1 && PyErr_Occurred())
+        return 0;
 
     field_name_is_empty = first->ptr >= first->end;