Issue #28253: Fixed calendar functions for extreme months: 0001-01 and 9999-12.

Methods itermonthdays() and itermonthdays2() are reimplemented so that they
don't call itermonthdates() which can cause datetime.date under/overflow.

1 files changed, 9 insertions, 10 deletions

diff --git a/Lib/calendar.py b/Lib/calendar.py
index 5244b8d..b5472f3 100644
--- a/Lib/calendar.py
+++ b/Lib/calendar.py
@@ -8,6 +8,7 @@ set the first day of the week (0=Monday, 6=Sunday)."""
 import sys
 import datetime
 import locale as _locale
+from itertools import repeat
 
 __all__ = ["IllegalMonthError", "IllegalWeekdayError", "setfirstweekday",
            "firstweekday", "isleap", "leapdays", "weekday", "monthrange",
@@ -174,22 +175,20 @@ class Calendar(object):
         Like itermonthdates(), but will yield (day number, weekday number)
         tuples. For days outside the specified month the day number is 0.
         """
-        for date in self.itermonthdates(year, month):
-            if date.month != month:
-                yield (0, date.weekday())
-            else:
-                yield (date.day, date.weekday())
+        for i, d in enumerate(self.itermonthdays(year, month), self.firstweekday):
+            yield d, i % 7
 
     def itermonthdays(self, year, month):
         """
         Like itermonthdates(), but will yield day numbers. For days outside
         the specified month the day number is 0.
         """
-        for date in self.itermonthdates(year, month):
-            if date.month != month:
-                yield 0
-            else:
-                yield date.day
+        day1, ndays = monthrange(year, month)
+        days_before = (day1 - self.firstweekday) % 7
+        yield from repeat(0, days_before)
+        yield from range(1, ndays + 1)
+        days_after = (self.firstweekday - day1 - ndays) % 7
+        yield from repeat(0, days_after)
 
     def monthdatescalendar(self, year, month):
         """