<p>对两列使用<a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.sort_values.html" rel="nofollow noreferrer">^{<cd1>}</a>,然后使用<a href="http://pandas.pydata.org/pandas-docs/stable/generated/pandas.core.groupby.GroupBy.tail.html" rel="nofollow noreferrer">^{<cd2>}</a>:</p>
<pre><code>df['servertime'] = pd.to_datetime(df['servertime'])
df1 = (df.sort_values(['session','servertime'])
.groupby('session', sort=False)
.tail(10))
print (df1)
session id servertime
0 1 3085 2018-10-09 13:20:25.096
1 1 3671 2018-10-21 08:19:39.078
2 1 2015 2018-10-23 21:22:27.647
5 7 4495 2018-10-31 04:50:56.864
6 7 5131 2018-11-04 10:49:03.044
7 7 4982 2018-11-04 12:02:03.738
8 7 4495 2018-11-04 12:43:53.595
9 7 3906 2018-11-05 16:55:17.891
10 7 8743 2018-11-06 16:55:17.891
11 7 6541 2018-11-07 16:55:17.891
12 7 3447 2018-11-08 16:55:17.891
13 7 6541 2018-11-08 18:55:17.891
14 7 1234 2018-11-09 16:55:17.891
15 20 10256 2018-08-28 11:09:35.902
16 20 11220 2018-09-09 06:49:48.440
17 20 5237 2018-09-13 12:01:09.677
18 20 5547 2018-09-13 12:02:34.762
19 20 6454 2018-09-13 12:07:40.061
</code></pre>