dataframe字符串转化为时间

from datetime import datetime
date = []
date_time = []
for dt in data['dt'].unique():
    date.append(dt)
    date_1 = datetime(int(dt[0:4]),int(dt[4:6]),int(dt[6:8]))
    date_time.append(date_1)

a = pd.DataFrame(date,columns=['date'])
b = DataFrame(date_time,columns=['date_time'])
date_con = pd.concat([a,b],axis=1)

data.merge(date_con,left_on='dt',right_on='date')