76 lines
2.1 KiB
Python
76 lines
2.1 KiB
Python
from abc import ABCMeta, abstractmethod
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class ChainLink(object, metaclass=ABCMeta):
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"""
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Abstract ChainLink object as part of the Chain of Responsibility pattern.
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- External Usage documentation: U{https://github.com/tylerlaberge/PyPatterns/wiki/Behavioral-Pattern-Usage}
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- External Chain of Responsibility Pattern documentation: U{https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern}
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"""
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def __init__(self):
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"""
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Initialize a new ChainLink instance.
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"""
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self.successor = None
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def set_successor(self, successor):
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"""
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Set a chain link to call if this chain link fails.
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@param successor: The chain link to call if this chain link fails.
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@type successor: ChainLink
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"""
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self.successor = successor
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def successor_handle(self, request):
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"""
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Have this chain links successor handle a request.
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@param request: The request to handle.
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"""
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return self.successor.handle(request)
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@abstractmethod
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def handle(self, request):
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"""
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Handle a request.
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@param request: The request to handle.
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"""
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pass
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class Chain(object, metaclass=ABCMeta):
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"""
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Abstract Chain class as part of the Chain of Responsibility pattern.
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- External Usage documentation: U{https://github.com/tylerlaberge/PyPatterns/wiki/Behavioral-Pattern-Usage}
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- External Chain of Responsibility Pattern documentation: U{https://en.wikipedia.org/wiki/Chain-of-responsibility_pattern}
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"""
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def __init__(self, chainlink):
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"""
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Initialize a new Chain instance.
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@param chainlink: The starting chain link.
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"""
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self.chainlink = chainlink
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def handle(self, request):
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"""
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Handle a request.
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@param request: The request to handle.
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"""
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try:
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return self.chainlink.handle(request)
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except AttributeError:
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return self.fail()
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@abstractmethod
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def fail(self):
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"""
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The method to call when the chain could not handle a request.
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"""
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pass
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