dataframe 时间列series 查看数值长度并统一

for i in range(row):
    length =len(str(data_time_index[i]))
    if length  ==4:
        data_time_index[i] = str(data_time_index[i])[:2]+':'+str(data_time_index[i])[2:]
    elif length ==3:
        data_time_index[i] = '0'+str(data_time_index[i])[0]+':'+str(data_time_index[i])[1:]
    elif length == 2:
        data_time_index[i] = '00' + ':' + str(data_time_index[i])[0:]
    elif length == 1:
        data_time_index[i] = '00' + ':' + '0'+str(data_time_index[i])[0:]
    else:
        data_time_index[i] ='999999'