Facade

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Facade Design Pattern in Python

Facade Design Pattern in Python

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What is it?

The Facade Design Pattern is a Structural Design Pattern. The word facade means the outerlying interface of a complex system, made up of several subsystems. In order to hide or abstract the complexities of the subsystems, a facade class is used. For example, while booting a computer system, many composite systems are initialized, such as processing unit, display unit, memory, peripherals. The facade in this case is the Power button located on the CPU.

It is classified under Structural Design Patterns as it offers one of the best ways to organize class hierarchy.

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Why the need for it: Problem Statement

In order to abstract the complexities of subsystems from the client, the Facade Pattern is employed.

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Terminology

• Facade: A class acting as an interface between the subsystems and client.

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Pseudo Code

The example below is hardly a useful one, but it helps to demonstrate the pattern. You can easily scale it to suit your needs.

class ProcessingUnit:
'''Subsystem #1'''

class DisplayUnit:
'''Subsystem #2'''

class Memory:
'''Subsystem #3'''

class Computer:
'''Facade'''
def __init__(self):
'''create objects of subsystems and assign to instance variables'''

def bootUp(self):
'''a method of facade which invokes relevant methods of subsystems'''

# USING THE CODE
create object of the facade
invoke method of facade which invokes relevant methods of subsystems


How to implement it
class ProcessingUnit:
'''Subsystem #1'''
def process(self):
print("Processing...")

class DisplayUnit:
'''Subsystem #2'''
def display(self):
print("Displaying...")

class Memory:
'''Subsystem #3'''
def ioOperation(self):
print("Reading and writing to memory...")

class Computer:
'''Facade'''
def __init__(self):
self.processingUnit = ProcessingUnit()
self.displayUnit = DisplayUnit()
self.memory = Memory()

def bootUp(self):
self.processingUnit.process()
self.memory.ioOperation()
self.displayUnit.display()

computer = Computer()
computer.bootUp()

As you can see, there is nothing complicated about the Facade Pattern. It is designed to hide the intricacy of a complex system by providing the client with a class which acts as an interface.


Creational Patterns
Factory
Abstract Factory
Prototype
Singleton
Builder


Structural Patterns
Decorator
Facade
Proxy
Composite
Adapter
Bridge


Behavioral Patterns
Visitor
Observer
Strategy
Iterator
Mediator
Chain of Responsibility


Architectural Pattern
Model View Controller (MVC)


See also:

Python 101
Object Oriented Python
50+ Handy Standard Library Modules
60+ Handy Third Library Modules
50+ Tips & Tricks for Python Developers
50+ Know-How(s) Every Pythonista Must Know