--- Lib/string.py	2012-02-17 09:47:29.682536857 +0530
+++ Lib/string.py       2012-02-17 09:47:29.682536857 +0530
@@ -188,6 +188,9 @@
     def _vformat(self, format_string, args, kwargs, used_args, recursion_depth):
         if recursion_depth < 0:
             raise ValueError('Max string recursion exceeded')
+        auto_field_count = 0
+        # manual numbering
+        manual = None
         result = []
         for literal_text, field_name, format_spec, conversion in \
                 self.parse(format_string):
@@ -200,7 +203,21 @@
             if field_name is not None:
                 # this is some markup, find the object and do
                 #  the formatting
-
+                
+                # automatic numbering
+                if field_name == "":
+                    if manual:
+                        raise ValueError("cannot switch from manual field specification to automatic field numbering")
+                    manual = False
+                    field_name = str(auto_field_count)
+                    auto_field_count += 1
+                    
+                # manual numbering
+                else:
+                    if manual is False:
+                        raise ValueError("cannot switch from automatic field numbering to manual field specification")
+                    manual = True
+                    
                 # given the field_name, find the object it references
                 #  and the argument it came from
                 obj, arg_used = self.get_field(field_name, args, kwargs)