title: Compute sum of rows in a new column Pandas
body: <p>I have a DataFrame as follow, where the column length can increase a lot. I am looking to create a new column based on the sum of each row</p>
  
  <pre><code>|---------------------|------------------|------------------|------------------|
  |        A            |         B        |         C        |      Total       |
  |---------------------|------------------|------------------|------------------|
  |        x            |         34       |         8        |        42        |
  |---------------------|------------------|------------------|------------------|
  |        y            |         43       |        12        |        55        |
  |---------------------|------------------|------------------|------------------|
  |        z            |         6        |         321      |        327       |
  |---------------------|------------------|------------------|------------------|
  
  </code></pre>
  
  <p>I know I can easily do: <code>df['Total'] = df['B'] + df['C']</code>
  However I am looking for a better technique as my column length can be very more important</p>