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• The chain of responsibility model
• Application scenarios
• Code example

The chain of responsibility model

The chain of responsibility model , Connect multiple processing methods into a chain , Requests will flow along the chain until a node in the chain can handle the request . Usually, this chain is formed by an object containing a reference to another object , Each node has a condition for the request , When the condition is not met, it will be passed to the next node for processing .

The responsibility chain model has several key points ：

1. An object contains a reference to another object, and so on to form a chain .
2. There should be a clear division of responsibilities in each object , That is, the condition for processing the request .
3. The last section of the chain should be designed for general request processing , To avoid loopholes .
4. The request should be passed into the head of the chain .

Application scenarios

Code example

Entity role ：

• Abstract processor （Handler）
• Specific handler （Concrete Handler）
• client （Client）

import abc
# Abstract processor 
class Handler(metaclass=abc.ABCMeta):
@abc.abstractmethod
def handle(self, day):
pass
# Specific handler , As one of the chain nodes .
class GeneralManager(Handler):
def handle(self, day):
if day <= 10:
print(f" The general manager granted leave {
day} God ")
else:
print(" Too long vacation , No leave ！")
# Specific handler , As one of the chain nodes .
class DivisionManager(Handler):
def __init__(self):
self.next = GeneralManager() # Link to the next level 
def handle(self, day):
if day <= 5:
print(f" The Department Manager granted leave {
day} God ")
else:
print(" Department managers are not qualified for leave ")
self.next.handle(day)
# Specific handler , As one of the chain nodes .
class ProjectManager(Handler):
def __init__(self):
self.next = DivisionManager() # Link to the next level 
def handle(self, day):
if day <= 3:
print(f" The project manager granted leave {
day} God ")
else:
print(" The project manager is not qualified for leave ")
self.next.handle(day)
if __name__ == "__main__":
handler = ProjectManager()
handler.handle(4)