title: Is it possible to inherit from an extension class in ODOO?
body: <p>On <code>addons/delivery/sale.py</code> we have a class that inherits <code>sale.order</code> at line 39:</p>
  
  <pre><code>class sale_order(osv.Model):
      _inherit = 'sale.order'
  </code></pre>
  
  <p>That's an extension class ( no <code>_name</code> )</p>
  
  <p>Is there a way to inherit from this class and rewrite one of is methods?</p>