#!/usr/bin/env pythpn
import datetime
now = datetime.datetime.now()
date_now = now.date()


def get_date_month(mon=0):
    last_m = (int(now.year) * 12 + int(now.month) - mon) % 12
    if len(str(last_m)) == 1:
        last_m = "%02d" % last_m
    last_y = int((int(now.year) * 12 + int(now.month) - mon) / 12)
    last_mon = '%s%s' % (last_y, last_m)

    return last_mon

last_mon = get_date_month(4);
print(last_mon)

$python get_year_month.py
202203