>>> import calendar >>> calendar.month(2024, -1) Traceback (most recent call last): File "<python-input-12>", line 1, in <module> calendar.month(2024, -1) ~~~~~~~~~~~~~~^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 395, in formatmonth for week in self.monthdays2calendar(theyear, themonth): ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 284, in monthdays2calendar days = list(self.itermonthdays2(year, month)) File "/Users/gugu/Code/cpython/Lib/calendar.py", line 240, in itermonthdays2 for i, d in enumerate(self.itermonthdays(year, month), self.firstweekday): ~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 228, in itermonthdays day1, ndays = monthrange(year, month) ~~~~~~~~~~^^^^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 165, in monthrange raise IllegalMonthError(month) calendar.IllegalMonthError: bad month number -1; must be 1-12 >>> calendar.month(2024, 13) Traceback (most recent call last): File "<python-input-13>", line 1, in <module> calendar.month(2024, 13) ~~~~~~~~~~~~~~^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 390, in formatmonth s = self.formatmonthname(theyear, themonth, 7 * (w + 1) - 1) File "/Users/gugu/Code/cpython/Lib/calendar.py", line 373, in formatmonthname s = month_name[themonth] ~~~~~~~~~~^^^^^^^^^^ File "/Users/gugu/Code/cpython/Lib/calendar.py", line 103, in __getitem__ funcs = self._months[i] ~~~~~~~~~~~~^^^ IndexError: list index out of range