title: All row sum with pandas except one
body: <p>I have several tables on a PostgreSQL database that look more or less like that:</p>
  
  <pre><code>gid      col2       col1        col3
  6        15         45          77
  1        15         45          57
  2        14         0.2         42
  3        12         6           37
  4        9          85          27
  5        5          1           15
  </code></pre>
  
  <p>For each table, numbers and columns' names change (I created them in a loop in python). </p>
  
  <p>I would like to have back another column called sum for each table with the sum of each calumn except for the gid. The goal is having something like that: </p>
  
  <pre><code>gid     col2       col1        col3     sum 
  6        15         45          77      137
  1        15         45          57      117
  2        14         0.2         42      56.2
  3        12         6           37      55
  4        9          85          27      121 
  5        5          1           15      21
  </code></pre>
  
  <p>I cannot use column name: the only one with no changes is <code>gid</code>.</p>
  
  <p>Some idea to make it with <code>python</code> (<code>pandas</code>, <code>numpy</code>) or <code>psql</code>?</p>