命令模式

在面向对象编程中，命令模式是概括所有方法信息的设计模式。命令模式封装了执行具体命令所需要的负载信息， 这样命令可以进一步扩展，如取消命令，撤销命令等。

命令模式是由三个组件构成，客户，调用者，接受者。

• 客户：一个实例化的对象
• 调用者：决定哪个方法被调用
• 接受者：实际命令的执行者

img

import time
import threading


class Chef(threading.Thread):
    def __init__(self,name):
        self.q = []
        self.doneq = []
        self.do_orders = True
        threading.Thread.__init__(self,)
        self.name = name
        self.start()

    def makeorder(self, order):
        print("%s Preparing Menu :"%self.name )
        for item in order.items:
            print("cooking ",item)
            time.sleep(1)
        order.completed = True
        self.doneq.append(order)

    def run(self,):
        while self.do_orders:
            if len(self.q) > 0:
                order = self.q.pop(0)
                self.makeorder(order)
                time.sleep(1)

    def work_on_order(self,order):
        self.q.append(order)

    def cancel(self, order):
        if order in self.q:
            if order.completed == True:
                print("cannot cancel, order completed")
                return
            else:
                index = self.q.index(order)
                del self.q[index]
                print(" order canceled %s"%str(order))
                return
        if order in self.doneq:
            print("order completed, cannot be canceled")
            return
        print("Order not given to me")


class Check(object):
    def execute(self,):
        raise NotImplementedError()

    def cancel(self,):
        raise NotImplementedError()


class MenuOrder(Check):
    def __init__(self,*items):
        self.items = items
        self.completed = False

    def execute(self,chef):
        self.chef = chef
        chef.work_on_order(self)

    def cancel(self,):
        if self.chef.cancel(self):
            print("order cancelled")
    
    def __str__(self,):
        return ''.join(self.items)

c = Chef("Arun")
order1 = MenuOrder("Omellette", "Dosa", "Idli")
order2 = MenuOrder("Mohito", "Pizza")
order3 = MenuOrder("Rajma", )
order1.execute(c)
order2.execute(c)
order3.execute(c)
time.sleep(1)
order3.cancel()
time.sleep(9)
c.do_orders = False
c.join()

输出结果如下：

Arun Preparing Menu :
('cooking ', 'Omellette')
 order canceled Rajma
('cooking ', 'Dosa')
('cooking ', 'Idli')
Arun Preparing Menu :
('cooking ', 'Mohito')
('cooking ', 'Pizza')