Odoo - prevent button from closing wizard

Question

I have a transient model that serves as a dialog. In my form view I have a button like this:

Answer 1

on odoo 7

def traszero(self ,cr ,uid ,ids ,context=None):
        data_obj = self.pool.get('stock.return.picking.line')
        ret_wizard = self.browse(cr, uid, ids, context=context)
        if ret_wizard.product_return_moves:
            line_ids = ret_wizard.product_return_moves.mapped('id')
            data_obj.write(cr, uid, line_ids, {'quantity': 0}, context=context)
        return {'name':"Return Shipment",
            'res_model':"stock.return.picking",
            'src_model':"stock.picking",
            'view_mode':"form",
            'target':"new",
            'key2':"client_action_multi",
            'multi':"True",
            'res_id':ids[0],
            'type': 'ir.actions.act_window',
            }