#!/usr/bin/env python

# -*- coding: utf-8 -*-

"""http://www.testingperspective.com/wiki/doku.php/collaboration/chetan/designpatternsinpython/chain-of-responsibilitypattern"""

class Handler:

def __init__(self):

self._successor = None

def successor(self, successor):

self._successor = successor

def handle(self, request):

raise NotImplementedError('Must provide implementation in subclass.')

class ConcreteHandler1(Handler):

def handle(self, request):

if 0 < request <= 10:

print('request {} handled in handler 1'.format(request))

elif self._successor:

self._successor.handle(request)

class ConcreteHandler2(Handler):

def handle(self, request):

if 10 < request <= 20:

print('request {} handled in handler 2'.format(request))

elif self._successor:

self._successor.handle(request)

class ConcreteHandler3(Handler):

def handle(self, request):

if 20 < request <= 30:

print('request {} handled in handler 3'.format(request))

elif self._successor:

self._successor.handle(request)

class DefaultHandler(Handler):

def handle(self, request):

print('end of chain, no handler for {}'.format(request))

class Client:

def __init__(self):

h1 = ConcreteHandler1()

h2 = ConcreteHandler2()

h3 = ConcreteHandler3()

h4 = DefaultHandler()

h1.successor(h2)

h2.successor(h3)

h3.successor(h4)

self.handlers = (h1, h2, h3, h4,)

def delegate(self, requests):

for request in requests:

self.handlers[0].handle(request)

if __name__ == "__main__":

client = Client()

requests = [2, 5, 14, 22, 18, 3, 35, 27, 20]

client.delegate(requests)

### OUTPUT ###

# request 2 handled in handler 1

# request 5 handled in handler 1

# request 14 handled in handler 2

# request 22 handled in handler 3

# request 18 handled in handler 2

# request 3 handled in handler 1

# end of chain, no handler for 35

# request 27 handled in handler 3

# request 20 handled in handler 2