4

How do I get the last Monday (or other day) of a given month?

user984003
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  • all I can think of is to iterate through every day of the month (descending) and asking if it's Monday. I was hoping for something simpler and shorter. – user984003 Oct 09 '12 at 09:04
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    Well, actually that is quite a good approach. However there is no need for iteration, you can use substraction. If the last day of the month (`lom`) is Wednesday (use `weekday()`), then you know that the Monday will be last day `lom - 2`. I am sure you can generalise upon that. – Hans Then Oct 09 '12 at 09:11

4 Answers4

9

Have a look at dateutil:

from datetime import datetime
from dateutil import relativedelta
datetime(2010,7,1) + relativedelta.relativedelta(day=31, weekday=relativedelta.MO(-1))

returns

datetime.datetime(2010, 7, 26, 0, 0)
eumiro
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8

Using the calendar module from the stdlib:

import calendar
cal = calendar.Calendar(0)
month = cal.monthdatescalendar(2010, 7)
lastweek = month[-1]
monday = lastweek[0]
print(monday)

2010-07-26
Gary van der Merwe
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    Unfortunately, this does not work for all cases. `lastweek` is a complete week (with first days of the following month if applicable), which for "last Sunday in July 2010" returns "2010-08-01". Try `lastweek[6]` – eumiro Oct 09 '12 at 10:39
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    @eumiro you are correct. One can give the day that your are looking for as the first day of week, so that you can always do lastweek[0], but that is messy. I think your dateutil answer is better. – Gary van der Merwe Oct 09 '12 at 11:16
  • this function fails in some cases, e.g. try getting last Friday of May, 2016, or last Wednesday of February, 2016 using this function – ierdna Mar 19 '16 at 01:29
  • I reckon the tidiest way to do this while preserving @GaryvanderMerwe's solution is to check the month: if the returned date's month is the previous, then take the following week, and the opposite for the last - e.g. let's say we want the first and last Mondays in May: `if last.month == 6: last = month[-2][0] if first.month == 4: first = month[1][0]` – puntofisso May 09 '18 at 15:03
3

Based on Gary's answer :

import calendar
month = calendar.monthcalendar(2010, 7)
mondays = [week[0] for week in month if week[0]>0]
print mondays[-1]

26

This works for getting the last Sunday of the month even if the last week of the month has no Sunday.

Community
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manu190466
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0

A tiny improvement on manu's answer !

import calendar
month = calendar.monthcalendar(2010, 7)
day_of_month = max(month[-1][calendar.SUNDAY], month[-2][calendar.SUNDAY])
print day_of_month
ticktock
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