Python gets the time of the previous few days

When processing files, sometimes data of a certain time range is often used.
For this situation of handwriting str every day, write a method call~

import datetime
def get_before_day(day, before):
    today = datetime.datetime.strptime(day, '%Y-%m-%d')
    offset = datetime.timedelta(days=-before)
    result = (today + offset).strftime('%Y-%m-%d')
    return result

for example:

get_before_day('2022-03-14', 1)
返回：'2022-03-13'