Generate a sequence of the last days of all previous N months with a given month

Question

Given a '%Y-%m' (e.g. 2022-03), what’s a good way to get a list of the last days of its previous N (e.g. 5) months with desired results:

['2021-10-31', '2021-11-30', '2021-12-31', '2022-01-31', '2022-02-28']

Asked By: Rock

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Source

Answer 1

As mentioned in comments, you can use a list comprehension to generate a list of previous month starts, then subtract one day from each of them.

def previous_month_ends(date, months):
  year, month, day = [int(x) for x in date.split('-')]
  d = datetime.date(year, month, day)
  t = datetime.timedelta(1)
  s = datetime.date(year, month, 1)
  return [(x - t).strftime('%Y-%m-%d')
          for m in range(months - 1, -1, -1)
          for x in (datetime.date(s.year, s.month - m, s.day) if s.month > m else 
                    datetime.date(s.year - 1, s.month - (m - 12), s.day),)]

You’ll want to do some math to ensure you handle the previous dates going into the previous year(s). The above will need to be modified to handle lartge values for months.

Answered By: Chris

Answer 2

I figured Pandas already has Month End (M) freq in its builtin date_range function:

>>> end = datetime.strptime('2022-03', '%Y-%m')
>>> start = end - pd.DateOffset(months=5)
>>> pd.date_range(start, end, freq='M')
DatetimeIndex(['2021-10-31', '2021-11-30', '2021-12-31', '2022-01-31', '2022-02-28'], dtype='datetime64[ns]', freq=None)

Answered By: Rock

Generate a sequence of the last days of all previous N months with a given month

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