i've created a module named "appointement" that have as fields -start-datetime- finish-datetime ... 

but when i try to overide the function name_get i got this error "AttributeError: type object 'appointment' has no attribute 'id'"

@api.multi
def name_get(self):
    result=[]
    for rd in self:
        name=rd.sujet+' faite par :'+rd.agent_id.name
        result.append((appointment.id,name))
    return result