get last billing date of previous month

relm.py

import datetime

from dateutil import relativedelta

import sys

try:

   input_date = sys.argv[1]

   input_date = datetime.datetime.strptime(input_date, "%Y-%m-%d").date()

   #This gives always last date of the month - relativedelta.relativedelta(day=31)

   prev_month = input_date - relativedelta.relativedelta(months=1) - relativedelta.relativedelta(day=31)

   print prev_month

except Exception, e:

   print e

Output:

python relm.py 2018-02-27 #2018-01-31

python relm.py 2018-12-28 #2018-11-30

python relm.py 2018-01-28 #2017-12-31

python relm.py 2018-02-31  #day is out of range for month