<p>我认为您误解了一些python语法,下面有两个任务:</p>
<pre><code>In [11]: a = b = 1
In [12]: a
Out[12]: 1
In [13]: b
Out[13]: 1
</code></pre>
<p>所以在你的代码中好像你在做:</p>
<pre><code>sum = df['budget'] + df['actual'] # a Series
# and
df['variance'] = df['budget'] + df['actual'] # assigned to a column
</code></pre>
<p>后者为df创建一个新列:</p>
<pre><code>In [21]: df
Out[21]:
cluster date budget actual
0 a 2014-01-01 00:00:00 11000 10000
1 a 2014-02-01 00:00:00 1200 1000
2 a 2014-03-01 00:00:00 200 100
3 b 2014-04-01 00:00:00 200 300
4 b 2014-05-01 00:00:00 400 450
5 c 2014-06-01 00:00:00 700 1000
6 c 2014-07-01 00:00:00 1200 1000
7 c 2014-08-01 00:00:00 200 100
8 c 2014-09-01 00:00:00 200 300
In [22]: df['variance'] = df['budget'] + df['actual']
In [23]: df
Out[23]:
cluster date budget actual variance
0 a 2014-01-01 00:00:00 11000 10000 21000
1 a 2014-02-01 00:00:00 1200 1000 2200
2 a 2014-03-01 00:00:00 200 100 300
3 b 2014-04-01 00:00:00 200 300 500
4 b 2014-05-01 00:00:00 400 450 850
5 c 2014-06-01 00:00:00 700 1000 1700
6 c 2014-07-01 00:00:00 1200 1000 2200
7 c 2014-08-01 00:00:00 200 100 300
8 c 2014-09-01 00:00:00 200 300 500
</code></pre>
<p>作为旁白,不应该使用<code>sum</code>作为变量名来重写内置的sum函数。</em></p>