【2016kindle】Learning Python Design Patterns，2e

1. class HealthCheck:
   
2.     _instance = None
   
3.     def __new__(cls, *args, **kwargs):
   
4.         if not HealthCheck._instance:
   
5.             HealthCheck._instance = super(HealthCheck, \
   
6.                 cls).__new__(cls, *args, **kwargs)
   
7.         return HealthCheck._instance
   
8.     def __init__(self):
   
9.         self._servers = []
   
10.     def addServer(self):
    
11.         self._servers.append("Server 1")
    
12.         self._servers.append("Server 2")
    
13.         self._servers.append("Server 3")
    
14.         self._servers.append("Server 4")
    
15.     def changeServer(self):
    
16.         self._servers.pop()
    
17.         self._servers.append("Server 5")
    
18. 
    
19. hc1 = HealthCheck()
    
20. hc2 = HealthCheck()
    
21. 
    
22. hc1.addServer()
    
23. print("Schedule health check for servers (1)..")
    
24. for i in range(4):
    
25.     print("Checking ", hc1._servers[i])
    
26. 
    
27. hc2.changeServer()
    
28. print("Schedule health check for servers (2)..")
    
29. for i in range(4):
    
30.     print("Checking ", hc2._servers[i])
    
31. The output of the code is as follows:

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1. from abc import ABCMeta, abstractmethod
   
2. 
   
3. class Animal(metaclass = ABCMeta):
   
4.     @abstractmethod
   
5.     def do_say(self):
   
6.         pass
   
7. 
   
8. class Dog(Animal):
   
9.     def do_say(self):
   
10.         print("Bhow Bhow!!")
    
11. 
    
12. class Cat(Animal):
    
13.     def do_say(self):
    
14.         print("Meow Meow!!")
    
15. 
    
16. 
    
17. ## forest factory defined
    
18. class ForestFactory(object):
    
19.     def make_sound(self, object_type):
    
20.         return eval(object_type)().do_say()
    
21. 
    
22. ## client code
    
23. if __name__ == '__main__':
    
24.     ff = ForestFactory()
    
25.     animal = input("Which animal should make_sound Dog or Cat?")
    
26.     ff.make_sound(animal)

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顶！！！！！！！！

好好学习

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感谢LZ的分享。呵呵

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