关于python:python-创建日期范围

def mkurl(self):        def create_assist_date(datestart=None, dateend=None):            if datestart is None:                datestart = '2016-01-01'            if dateend is None:                dateend = datetime.datetime.now().strftime('%Y-%m-%d')            # 转为日期格局            datestart = datetime.datetime.strptime(datestart, '%Y-%m-%d')            dateend = datetime.datetime.strptime(dateend, '%Y-%m-%d')            date_list = []            date_list.append(datestart.strftime('%Y-%m-%d'))            while datestart < dateend:                # 日期叠加一天                datestart += datetime.timedelta(days=+1)                # 日期转字符串存入列表                date_list.append(datestart.strftime('%Y-%m-%d'))            return [i.replace('-', '') for i in date_list]        for i in create_assist_date("2018-12-31", "2020-01-01"):            yield self.listurl.format(i)