from datetime import datetime
def get_date(date: str):
    pattern = '%Y-%m-%d'
    return datetime.strptime(date, pattern)
date_1 = get_date('2020-03-11')
date_2 = get_date('2020-05-25')
delta = date_2 - date_1
print(delta.days)

  
>>> import datetime
>>> 
>>> date1 = datetime.datetime(2020, 3, 12)
>>> date2 = datetime.datetime(2021, 4, 15)
>>> delta = date2 - date1
>>> delta
datetime.timedelta(399)
>>> delta.days
399
>>> 
>>> date1 + datetime.timedelta(days=30)
datetime.datetime(2020, 4, 11, 0, 0)
>>>