class sale_order(osv.Model):
    _inherit = 'sale.order'

#Original definition v8 addons/delivery/sale.py  line no 36 :
class sale_order(osv.Model):
    _name = "sale.order"
#Example method on sale order calss line #601
def action_wait(self, cr, uid, ids, context=None):

#Original definition v8 /addons/sale_stock/sale_stock.py  line no 30 :
class sale_order(osv.Model):
    _name = "sale.order"

 #this is method originally defined in parent class and being over-ride here,
def action_wait(self, cr, uid, ids, context=None):
    #Your Code goes here
    res = super(sale_order, self).action_wait(cr, uid, ids, context=context)
    #Your Code goes here
    return res