title: Select as in sqlalchemy
body: <p>I want to do something like this:</p>
  
  <pre><code>select username, userid, 'user' as new_column  from  users_table.
  </code></pre>
  
  <p>The columns of the table can be selected using sqlalchemy as follows:</p>
  
  <pre><code>query = select([users_table.c.username, users_table.c.userid])
  </code></pre>
  
  <p>How do I do the select <code>x</code> as <code>col_x</code> to the query in sqlalchemy?</p>