Source Code for Module pypat.behavioral.chain

 1  from abc import ABCMeta, abstractmethod 
 2   
 3   
 4 -class ChainLink(object, metaclass=ABCMeta): 
 5      """ 
 6      Abstract ChainLink object as part of the Chain of Responsibility pattern. 
 7   
 8      - External Usage documentation: U{https://github.com/tylerlaberge/PyPatterns/wiki/Behavioral-Pattern-Usage} 
 9      - External Chain of Responsibility Pattern documentation: U{https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern} 
10      """ 
11 -    def __init__(self): 
12          """ 
13          Initialize a new ChainLink instance. 
14          """ 
15          self.successor = None 
16   
17 -    def set_successor(self, successor): 
18          """ 
19          Set a chain link to call if this chain link fails. 
20   
21          @param successor: The chain link to call if this chain link fails. 
22          @type successor: ChainLink 
23          """ 
24          self.successor = successor 
25   
26 -    def successor_handle(self, request): 
27          """ 
28          Have this chain links successor handle a request. 
29   
30          @param request: The request to handle. 
31          """ 
32          return self.successor.handle(request) 
33   
34      @abstractmethod 
35 -    def handle(self, request): 
36          """ 
37          Handle a request. 
38   
39          @param request: The request to handle. 
40          """ 
41          pass 
42   
43   
44 -class Chain(object, metaclass=ABCMeta): 
45      """ 
46      Abstract Chain class as part of the Chain of Responsibility pattern. 
47   
48      - External Usage documentation: U{https://github.com/tylerlaberge/PyPatterns/wiki/Behavioral-Pattern-Usage} 
49      - External Chain of Responsibility Pattern documentation: U{https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern} 
50      """ 
51 -    def __init__(self, chainlink): 
52          """ 
53          Initialize a new Chain instance. 
54   
55          @param chainlink: The starting chain link. 
56          """ 
57          self.chainlink = chainlink 
58   
59 -    def handle(self, request): 
60          """ 
61          Handle a request. 
62   
63          @param request: The request to handle. 
64          """ 
65          try: 
66              return self.chainlink.handle(request) 
67          except AttributeError: 
68              return self.fail() 
69   
70      @abstractmethod 
71 -    def fail(self): 
72          """ 
73          The method to call when the chain could not handle a request. 
74          """ 
75          pass 
76