title: Removing quotes in string interpolation
body: <p>In Python, I am building a string to be used as a condition in another function.      </p>
  
  <pre><code>po_id_criteria = "('id','='," + str(ids[0]) + ")"
  po_ids = po_obj.search(cr, uid, [('state','in',['sourced','confirmed','confirmed_wait','approved']),po_id_criteria])
  </code></pre>
  
  <p>And get an error, because the double quotes are being added:</p>
  
  <pre><code>ValueError: Bad domain expression: [('active', '=', 1), ('state', 'in', ['sourced', 'confirmed', 'confirmed_wait', 'approved']), "('id','=',1)"]
  </code></pre>
  
  <p>I really want it without the double quotes, ie:</p>
  
  <pre><code>[('active', '=', 1), ('state', 'in', ['sourced', 'confirmed', 'confirmed_wait', 'approved']), ('id','=',1)]
  </code></pre>