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Design Patterns - Decorator in Python
Jigisha Sata
a year ago
Table of Content
- Implementation of Decorator Design Pattern
- Output
With
the help of Decorator, we can add new functionality to an existing object
without altering.
This
design pattern comes under structural pattern and acts as a wrapper to existing
class.
It
creates a decorator class, which wraps the original class and provides
additional functionality keeping the class methods signature intact.
The
main aim of a decorator is to provides additional responsibilities of an object
dynamically.
Implementation of Decorator Design Pattern
Let’s
take a simple demonstration of how to implement a decorator design pattern in
python.
An example involves the demonstration of a coffee shop in the format of the class.
The created coffee class is abstract, which means it cannot be instantiated.
import six
from abc import ABCMeta
@six.add_metaclass(ABCMeta)
class Abstract_Coffee(object):
def get_cost(self):
pass
def get_ingredients(self):
pass
def get_tax(self):
return 0.1*self.get_cost()
class Concrete_Coffee(Abstract_Coffee):
def get_cost(self):
return 1.00
def get_ingredients(self):
return 'coffee'
@six.add_metaclass(ABCMeta)
class Abstract_Coffee_Decorator(Abstract_Coffee):
def __init__(self,decorated_coffee):
self.decorated_coffee = decorated_coffee
def get_cost(self):
return self.decorated_coffee.get_cost()
def get_ingredients(self):
return self.decorated_coffee.get_ingredients()
class Sugar(Abstract_Coffee_Decorator):
def __init__(self,decorated_coffee):
Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
def get_cost(self):
return self.decorated_coffee.get_cost()
def get_ingredients(self):
return self.decorated_coffee.get_ingredients() + ', sugar'
class Milk(Abstract_Coffee_Decorator):
def __init__(self,decorated_coffee):
Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
def get_cost(self):
return self.decorated_coffee.get_cost() + 0.25
def get_ingredients(self):
return self.decorated_coffee.get_ingredients() + ', milk'
class Vanilla(Abstract_Coffee_Decorator):
def __init__(self,decorated_coffee):
Abstract_Coffee_Decorator.__init__(self,decorated_coffee)
def get_cost(self):
return self.decorated_coffee.get_cost() + 0.75
def get_ingredients(self):
return self.decorated_coffee.get_ingredients() + ', vanilla'The
implementation of the abstract class of the coffee shop is done with a separate
file as mentioned below −
import coffeeshop
myCoffee = coffeeshop.Concrete_Coffee()
print('Ingredients: '+myCoffee.get_ingredients()+
'; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Milk(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
'; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Vanilla(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
'; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))
myCoffee = coffeeshop.Sugar(myCoffee)
print('Ingredients: '+myCoffee.get_ingredients()+
'; Cost: '+str(myCoffee.get_cost())+'; sales tax = '+str(myCoffee.get_tax()))Output
The
output of the above example code is –
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