import datetime

ref_date = "2021-02-7"

ref_date_date = datetime.datetime.strptime(ref_date, '%Y-%m-%d')

print(ref_date)

firstday_refmonth = ref_date_date.replace(day=1)

next_month = ref_date_date.replace(day=28) + datetime.timedelta(days=4)
lastday_refmonth = next_month - datetime.timedelta(days=next_month.day) 

firstday_refmonth_str = datetime.datetime.strftime(firstday_refmonth, '%Y-%m-%d')
lastday_refmonth_str = datetime.datetime.strftime(lastday_refmonth, '%Y-%m-%d')

print(firstday_refmonth_str)
print(lastday_refmonth_str)

##########################################

import datetime
from dateutil.relativedelta import relativedelta

def get_days(ref_date):
  ref_date_date = datetime.datetime.strptime(ref_date, '%Y-%m-%d')


  date = ref_date_date + datetime.timedelta(days=1)
  date = ref_date_date + relativedelta(months=-1)
  

  firstday_refmonth = date.replace(day=1)

  next_month = date.replace(day=28) + datetime.timedelta(days=4)
  lastday_refmonth = next_month - datetime.timedelta(days=next_month.day) 

  first_day = datetime.datetime.strftime(firstday_refmonth, '%Y-%m-%d')
  last_day = datetime.datetime.strftime(lastday_refmonth, '%Y-%m-%d')

  return first_day, last_day


get_days("2021-02-01")