一些场景需要第一天或者最后一天进行脚本操作，如签到，下面代码可判断第一天和最后一天
from dateutil.relativedelta import relativedelta
import datetime
today = datetime.datetime.today()
# 第一天
first_day=(relativedelta() + today).replace(day=1)
print (first_day)
# 最后一天
last_day = (relativedelta(months=1) + today).replace(day=1) - relativedelta(days=1)
print ( last_day)
if today==first_day:
print ("第一天")
if today==last_day:
print ("最后一天")