title: Add column to dataframe with constant value
body: <p>I have an existing dataframe which I need to add an additional column to which will contain the same value for every row.</p>
  
  <p>Existing df:</p>
  
  <pre><code>Date, Open, High, Low, Close
  01-01-2015, 565, 600, 400, 450
  </code></pre>
  
  <p>New df:</p>
  
  <pre><code>Name, Date, Open, High, Low, Close
  abc, 01-01-2015, 565, 600, 400, 450
  </code></pre>
  
  <p>I know how to append an existing series / dataframe column. But this is a different situation, because all I need is to add the 'Name' column and set every row to the same value, in this case 'abc'.</p>