获取两个日期之间的月份数
from datetime import datetime
start_date = datetime.strptime('2021-01', '%Y-%m')
start_year, start_month = start_date.year, start_date.month
end_date = datetime.strptime('2021-09', '%Y-%m')
end_year, end_month = end_date.year, end_date.month
interval=