python datetime 转换

import datetime
def datetransfer(nowtime):
    # now_time = datetime.datetime.now()
    if '-' in nowtime:
        # _d_time = datetime.datetime.strptime(nowtime, '%Y-%m-%d %H:%M:%S')
        _d_time = datetime.datetime.strptime(nowtime, '%Y-%m-%d')
        f_time = datetime.datetime.strftime(_d_time, '%Y/%m/%d')
        print(f_time)
        return f_time
    if '/' in nowtime:
        return nowtime
    else:
        _d_time = datetime.datetime.strptime(nowtime, '%Y%m%d')
        f_time = datetime.datetime.strftime(_d_time, '%Y/%m/%d')
        print(f_time)
        return f_time

def returnoneday(day):
    return (datetime.datetime.now() + datetime.timedelta(days=day)).strftime("%Y/%m/%d")