title: Pandas: sum up multiple columns into one column without last column
body: <p>If I have a dataframe similar to this one</p>
  
  <pre><code>Apples   Bananas   Grapes   Kiwis
  2        3         nan      1
  1        3         7        nan
  nan      nan       2        3
  </code></pre>
  
  <p>I would like to add a column like this</p>
  
  <pre><code>Apples   Bananas   Grapes   Kiwis   Fruit Total
  2        3         nan      1        6
  1        3         7        nan      11
  nan      nan       2        3        5
  </code></pre>
  
  <p>I guess you could use <code>df['Apples'] + df['Bananas']</code> and so on, but my actual dataframe is much larger than this. I was hoping a formula like <code>df['Fruit Total']=df[-4:-1].sum</code> could do the trick in one line of code. That didn't work however. Is there any way to do it without explicitly summing up all columns?</p>