class Data(object):

""" Data Store Class """

products = {

'milk': {'price': 1.50, 'quantity': 10},

'eggs': {'price': 0.20, 'quantity': 100},

'cheese': {'price': 2.00, 'quantity': 10}

}

def __get__(self, obj, klas):

print ("(Fetching from Data Store)")

return {'products': self.products}

class BusinessLogic(object):

""" Business logic holding data store instances """

data = Data()

def product_list(self):

return self.data['products'].keys()

def product_information(self, product):

return self.data['products'].get(product, None)

class Ui(object):

""" UI interaction class """

def __init__(self):

self.business_logic = BusinessLogic()

def get_product_list(self):

print('PRODUCT LIST:')

for product in self.business_logic.product_list():

#print(product)

yield product

print('')

def get_product_information(self, product):

if __name__ == '__main__':

main()

python-patterns

A collection of design patterns and idioms in Python.

When an implementation is added or modified, be sure to update this file and

rerun `append_output.sh` (eg. ./append_output.sh borg.py) to keep the output

comments at the bottom up to date.

Current Patterns:

| Pattern | Description |

|:-------:| ----------- |

| [3-tier](3-tier.py) | data<->business logic<->presentation separation (strict relationships) |

| [abstract_factory](abstract_factory.py) | use a generic function with specific factories |

| [adapter](adapter.py) | adapt one interface to another using a whitelist |

| [borg](borg.py) | a singleton with shared-state among instances |

| [bridge](bridge.py) | a client-provider middleman to soften interface changes |

| [builder](builder.py) | call many little discrete methods rather than having a huge number of constructor parameters |

| [catalog](catalog.py) | general methods will call different specialized methods based on construction parameter |

| [chain](chain.py) | apply a chain of successive handlers to try and process the data |

| [command](command.py) | bundle a command and arguments to call later |

| [composite](composite.py) | encapsulate and provide access to a number of different objects |

| [decorator](decorator.py) | wrap functionality with other functionality in order to affect outputs |

| [facade](facade.py) | use one class as an API to a number of others |

| [factory_method](factory_method.py) | delegate a specialized function/method to create instances |

| [flyweight](flyweight.py) | transparently reuse existing instances of objects with similar/identical state |

| [graph_search](graph_search.py) | (graphing algorithms, not design patterns) |

| [mediator](mediator.py) | an object that knows how to connect other objects and act as a proxy |

| [memento](memento.py) | generate an opaque token that can be used to go back to a previous state |

| [mvc](mvc.py) | model<->view<->controller (non-strict relationships) |

| [observer](observer.py) | provide a callback for notification of events/changes to data |

| [pool](pool.py) | preinstantiate and maintain a group of instances of the same type |

| [prototype](prototype.py) | use a factory and clones of a prototype for new instances (if instantiation is expensive) |

| [proxy](proxy.py) | an object funnels operations to something else |

| [publish_subscribe](publish_subscribe.py) | a source syndicates events/data to 0+ registered listeners |

| [state](state.py) | logic is org'd into a discrete number of potential states and the next state that can be transitioned to |

| [strategy](strategy.py) | selectable operations over the same data |

| [template](template.py) | an object imposes a structure but takes pluggable components |

| [visitor](visitor.py) | invoke a callback for all items of a collection |

| [chaining_method](chaining_method.py) | continue callback next object method |

import random

class PetShop:

"""A pet shop"""

def __init__(self, animal_factory=None):

"""pet_factory is our abstract factory. We can set it at will."""

self.pet_factory = animal_factory

def show_pet(self):

"""Creates and shows a pet using the abstract factory"""

pet = self.pet_factory.get_pet()

print("We have a lovely {}".format(pet))

print("It says {}".format(pet.speak()))

print("We also have {}".format(self.pet_factory.get_food()))

class Dog:

def speak(self):

return "woof"

class Cat:

def speak(self):

return "meow"

class DogFactory:

def get_pet(self):

return Dog()

class CatFactory:

def get_pet(self):

return Cat()

def get_food(self):

return "cat food"

def get_factory():

"""Let's be dynamic!"""

if __name__ == "__main__":

for i in range(3):

shop = PetShop(get_factory())

shop.show_pet()

print("=" * 20)

import os

class Dog(object):

def __init__(self):

self.name = "Dog"

def bark(self):

return "woof!"

class Cat(object):

def __init__(self):

self.name = "Cat"

def meow(self):

return "meow!"

class Human(object):

def __init__(self):

self.name = "Human"

def speak(self):

return "'hello'"

class Car(object):

def __init__(self):

self.name = "Car"

def make_noise(self, octane_level):

return "vroom{0}".format("!" * octane_level)

class Adapter(object):

"""

def __init__(self, obj, adapted_methods):

"""We set the adapted methods in the object's dict"""

self.obj = obj

if __name__ == "__main__":

main()

set -e

src=$(sed -n -e '/### OUTPUT ###/,$!p' "$1")

output=$(python "$1" | sed 's/^/# /')

echo "$src" > $1

echo -e "\n### OUTPUT ###" >> $1

echo "$output" >> $1

class Borg:

__shared_state = {}

def __init__(self):

self.__dict__ = self.__shared_state

self.state = 'Init'

def __str__(self):

return self.state

rm1.state = 'Idle'

rm2.state = 'Running'

print('rm1: {0}'.format(rm1))

print('rm2: {0}'.format(rm2))

rm2.state = 'Zombie'

print('rm1: {0}'.format(rm1))

print('rm2: {0}'.format(rm2))

print('rm1 id: {0}'.format(id(rm1)))

print('rm2 id: {0}'.format(id(rm2)))

rm3 = YourBorg()

print('rm1: {0}'.format(rm1))

print('rm2: {0}'.format(rm2))

print('rm3: {0}'.format(rm3))