make _localized_name instances work more like the tuples they replaced. In

particular, negative indexes work and they are limited by the actual length
of the names they represent (weekday and month names).  This closes bug
#503202.

Lib/calendar.py

@@ -25,18 +25,25 @@ February = 2
 mdays = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
 
 class _localized_name:
-    def __init__(self, format):
+    def __init__(self, format, len):
         self.format = format
+        self.len = len
     def __getitem__(self, item):
+        if item > self.len-1 or item < -self.len:
+            raise IndexError
+        if item < 0:
+            item += self.len
         return strftime(self.format, (item,)*9).capitalize()
+    def __len__(self):
+        return self.len
 
 # Full and abbreviated names of weekdays
-day_name = _localized_name('%A')
-day_abbr = _localized_name('%a')
+day_name = _localized_name('%A', 7)
+day_abbr = _localized_name('%a', 7)
 
 # Full and abbreviated names of months (1-based arrays!!!)
-month_name = _localized_name('%B')
-month_abbr = _localized_name('%b')
+month_name = _localized_name('%B', 12)
+month_abbr = _localized_name('%b', 12)
 
 # Constants for weekdays
 (MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY) = range(7)