Changed signature of string.Formatter.get_field, per suggestion by

Ron Adam.

Added test case for using all parameters in string.Formatter.

Lib/string.py

@@ -208,7 +208,7 @@ class Formatter:
         return self.vformat(format_string, args, kwargs)
 
     def vformat(self, format_string, args, kwargs):
-        used_args = self.get_empty_used_args()
+        used_args = set()
         result = []
         for literal_text, field_name, format_spec, conversion in \
                 self.parse(format_string):
@@ -223,7 +223,9 @@ class Formatter:
                 #  the formatting
 
                 # given the field_name, find the object it references
-                obj = self.get_field(field_name, args, kwargs, used_args)
+                #  and the argument it came from
+                obj, arg_used = self.get_field(field_name, args, kwargs, used_args)
+                used_args.add(arg_used)
 
                 # do any conversion on the resulting object
                 obj = self.convert_field(obj, conversion)
@@ -235,10 +237,6 @@ class Formatter:
         return ''.join(result)
 
 
-    def get_empty_used_args(self):
-        return set()
-
-
     def get_value(self, key, args, kwargs):
         if isinstance(key, int):
             return args[key]
@@ -296,4 +294,4 @@ class Formatter:
             else:
                 obj = obj[i]
 
-        return obj
+        return obj, first

Lib/test/test_string.py

@@ -79,6 +79,28 @@ class ModuleTest(unittest.TestCase):
         fmt = BarFormatter()
         self.assertEqual(fmt.format('*|+0:^10s|*', 'foo'), '*   foo    *')
 
+        # test all parameters used
+        class CheckAllUsedFormatter(string.Formatter):
+            def check_unused_args(self, used_args, args, kwargs):
+                # Track which arguments actuallly got used
+                unused_args = set(kwargs.keys())
+                unused_args.update(range(0, len(args)))
+
+                for arg in used_args:
+                    unused_args.remove(arg)
+
+                if unused_args:
+                    raise ValueError("unused arguments")
+
+        fmt = CheckAllUsedFormatter()
+        self.assertEqual(fmt.format("{0}", 10), "10")
+        self.assertEqual(fmt.format("{0}{i}", 10, i=100), "10100")
+        self.assertEqual(fmt.format("{0}{i}{1}", 10, 20, i=100), "1010020")
+        self.assertRaises(ValueError, fmt.format, "{0}{i}{1}", 10, 20, i=100, j=0)
+        self.assertRaises(ValueError, fmt.format, "{0}", 10, 20)
+        self.assertRaises(ValueError, fmt.format, "{0}", 10, 20, i=100)
+        self.assertRaises(ValueError, fmt.format, "{i}", 10, 20, i=100)
+
 
     def test_maketrans(self):
         transtable = '\000\001\002\003\004\005\006\007\010\011\012\013\014\015\016\017\020\021\022\023\024\025\026\027\030\031\032\033\034\035\036\037 !"#$%&\'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\\]^_`xyzdefghijklmnopqrstuvwxyz{|}~\177\200\201\202\203\204\205\206\207\210\211\212\213\214\215\216\217\220\221\222\223\224\225\226\227\230\231\232\233\234\235\236\237\240\241\242\243\244\245\246\247\250\251\252\253\254\255\256\257\260\261\262\263\264\265\266\267\270\271\272\273\274\275\276\277\300\301\302\303\304\305\306\307\310\311\312\313\314\315\316\317\320\321\322\323\324\325\326\327\330\331\332\333\334\335\336\337\340\341\342\343\344\345\346\347\350\351\352\353\354\355\356\357\360\361\362\363\364\365\366\367\370\371\372\373\374\375\376\377'