Get the last day of the month

Question

Is there a way using Python's standard library to easily determine (i.e. one function call) the last day of a given month?

If the standard library doesn't support that, does the dateutil package support this?

Answer 1

calendar.monthrange provides this information:

calendar.monthrange(year, month)
    Returns weekday of first day of the month and number of days in month, for the specified year and month.

>>> import calendar
>>> calendar.monthrange(2002, 1)
(calendar.TUESDAY, 31)

>>> calendar.monthrange(2008, 2)  # leap years are handled correctly
(calendar.FRIDAY, 29)

>>> calendar.monthrange(2100, 2)  # years divisible by 100 but not 400 aren't leap years
(calendar.MONDAY, 28)

# the module uses the Georgian calendar extended into the past and
# future, so leap days in the distant past will differ from Julian:
>>> calendar.monthrange(1100, 2)
(calendar.THURSDAY, 28)

# note also that pre-Python 3.12, the REPL renders the weekday
# as a bare integer:
>>> calendar.monthrange(2002, 1)
(1, 31)

so:

calendar.monthrange(year, month)[1]

seems like the simplest way to go.