$ python Main.py 
[Trouble 0] is resolved by [Bob].
[Trouble 33] is resolved by [Bob].
[Trouble 66] is resolved by [Bob].
[Trouble 99] is resolved by [Bob].
[Trouble 132] is resolved by [Diana].
[Trouble 165] is resolved by [Diana].
[Trouble 198] is resolved by [Diana].
[Trouble 231] is resolved by [Elmo].
[Trouble 264] is resolved by [Fred].
[Trouble 297] is resolved by [Elmo].
[Trouble 330] cannot be resolved.
[Trouble 363] is resolved by [Elmo].
[Trouble 396] cannot be resolved.
[Trouble 429] is resolved by [Charlie].
[Trouble 462] cannot be resolved.
[Trouble 495] is resolved by [Elmo].

Somehow, the output result was difficult to understand. To understand the output result of the sample program, it seems faster to check the details of the sample program.

■ Details of sample program

Similar code has been uploaded to the Git repository. https://github.com/ttsubo/study_of_design_pattern/tree/master/Chain_of_Responsibility

--Directory structure

.
├── Main.py
├── support.py
└── trouble.py

(1) The role of Handler

The Handler role defines the interface for processing requests. Keep the "next person", and if you receive a request that you cannot handle, you can send it to that person. Of course, the "next person" also plays the role of Handler. In the sample program, the Support class serves this role. The method that handles the request was the support method.

support.py

from abc import ABCMeta, abstractmethod

class Support(metaclass=ABCMeta):
    def __init__(self, name):
        self.__name = name
        self.__next = None

    def setNext(self, next):
        self.__next = next
        return next

    def support(self, trouble):
        if self.resolve(trouble):
            self.done(trouble)
        elif self.__next is not None:
            self.__next.support(trouble)
        else:
            self.fail(trouble)

    def __str__(self):
        return "[{0}]".format(self.__name)

    @abstractmethod
    def resolve(self, trouble):
        pass

    def done(self, trouble):
        print("{0} is resolved by {1}.".format(trouble, self))

    def fail(self, trouble):
        print("{0} cannot be resolved.".format(trouble))

(2) The role of ConcreteHandler

The ConcreteHandler role is a specific role for processing a request. In the sample program, the NoSupport, LimitSupport, ʻOddSupport, and SpecialSupport` classes serve this role.

support.py

class NoSupport(Support):
    def __init__(self, name):
        super(NoSupport, self).__init__(name)

    def resolve(self, trouble):
        return False

class LimitSupport(Support):
    def __init__(self, name, limit):
        super(LimitSupport, self).__init__(name)
        self.__limit = limit

    def resolve(self, trouble):
        return True if trouble.getNumber() < self.__limit else False

class OddSupport(Support):
    def __init__(self, name):
        super(OddSupport, self).__init__(name)

    def resolve(self, trouble):
        return True if trouble.getNumber() % 2 == 1 else False

class SpecialSupport(Support):
    def __init__(self, name, number):
        super(SpecialSupport, self).__init__(name)
        self.__number = number

    def resolve(self, trouble):
        return True if trouble.getNumber() == self.__number else False

(3) The role of Client

The Client role is the role that makes a request to the first ConcreteHandler role. In the sample program, the startMain method serves this role.

Main.py

from support import NoSupport, LimitSupport, SpecialSupport, OddSupport
from trouble import Trouble

def startMain():
    alice = NoSupport("Alice")
    bob = LimitSupport("Bob", 100)
    charlie = SpecialSupport("Charlie", 429)
    diana = LimitSupport("Diana", 200)
    elmo = OddSupport("Elmo")
    fred = LimitSupport("Fred", 300)

    alice.setNext(bob).setNext(charlie).setNext(diana).setNext(elmo).setNext(fred)

    for i in range(0, 500, 33):
        alice.support(Trouble(i))

if __name__ == '__main__':
    startMain()

(4) Other

Centrally manage trouble numbers.

trouble.py

class Trouble:
    def __init__(self, number):
        self.__number = number

    def getNumber(self):
        return self.__number

    def __str__(self):
        return '[Trouble {0}]'.format(self.__number)

■ Reference URL

-[Finishing "Introduction to Design Patterns Learned in Java Language" (Not)](https://medium.com/since-i-want-to-start-blog-that-looks-like-men-do/java Introduction to Design Patterns Learned in Language-Finishing-Not-2cc9b34a30b2)