diff -r 5073fa30f226 Lib/datetime.py
--- a/Lib/datetime.py	Tue Nov 12 10:03:20 2013 -0500
+++ b/Lib/datetime.py	Tue Nov 12 23:01:37 2013 +0530
@@ -44,7 +44,7 @@
 
 def _days_in_month(year, month):
     "year, month -> number of days in that month in that year."
-    assert 1 <= month <= 12, month
+    assert 1 <= month <= 12,'month must be in 1..12'
     if month == 2 and _is_leap(year):
         return 29
     return _DAYS_IN_MONTH[month]