数据帧字典中的最大值和最小日期

问：

在每个数据帧的字典中查找最大和最小日期的最 pythonic 方法是什么？例如：

import pandas as pd
import datetime

df1 = pd.DataFrame(index =  [datetime.datetime(2016, 7, 2, 0, 0),
                    datetime.datetime(2016, 8, 6, 0, 0),
                    datetime.datetime(2016, 9, 13, 0, 0),
                    datetime.datetime(2016, 10, 26, 0, 0),
                    datetime.datetime(2016, 11, 2, 0, 0)],
                    data = {'bee' : [5, 3, 1, 0, 2],
                           'an' : [2,3,2,2,7]})

df2 = pd.DataFrame(index =  [datetime.datetime(2015, 7, 2, 0, 0),
                    datetime.datetime(2015, 8, 6, 0, 0),
                    datetime.datetime(2015, 9, 13, 0, 0),
                    datetime.datetime(2015, 10, 26, 0, 0),
                    datetime.datetime(2015, 11, 2, 0, 0)],
                    data = {'bee' : [15, 2, 5, 0, 2],
                           'an' : [1,1,2,7,7]})

df_dict = {'df1':df1, 'df2':df2}

df_dict['df1']

输出：

index       an  bee
2016-07-02  2   5
2016-08-06  3   3
2016-09-13  2   1
2016-10-26  2   0
2016-11-02  7   2

和

df_dict['df2']

输出

index       an  bee
2015-07-02  1   15
2015-08-06  1   2
2015-09-13  2   5
2015-10-26  7   0
2015-11-02  7   2

所以，我想找到 的最大日期 ，应该是 2016-11-02，最短日期是 ，应该是 2015-07-02。df_dictdf_dict