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"""

Example from https://en.wikipedia.org/wiki/Facade_pattern#Python

*What is this pattern about?

The Facade pattern is a way to provide a simpler unified interface to

a more complex system. It provides an easier way to access functions

of the underlying system by providing a single entry point.

This kind of abstraction is seen in many real life situations. For

example, we can turn on a computer by just pressing a button, but in

fact there are many procedures and operations done when that happens

(e.g., loading programs from disk to memory). In this case, the button

serves as an unified interface to all the underlying procedures to

turn on a computer.

*Where is the pattern used practically?

This pattern can be seen in the Python standard library when we use

the isdir function. Although a user simply uses this function to know

whether a path refers to a directory, the system makes a few

operations and calls other modules (e.g., os.stat) to give the result.

*References:

https://sourcemaking.com/design_patterns/facade

https://fkromer.github.io/python-pattern-references/design/#facade

http://python-3-patterns-idioms-test.readthedocs.io/en/latest/ChangeInterface.html#facade

*TL;DR

Provides a simpler unified interface to a complex system.

"""

# Complex computer parts

class CPU:

"""

Simple CPU representation.

"""

def freeze(self):

print("Freezing processor.")

def jump(self, position):

print("Jumping to:", position)

def execute(self):

print("Executing.")

class Memory:

"""

Simple memory representation.

"""

def load(self, position, data):

print("Loading from {0} data: '{1}'.".format(position, data))

class SolidStateDrive:

"""

Simple solid state drive representation.

"""

def read(self, lba, size):

return "Some data from sector {0} with size {1}".format(lba, size)

class ComputerFacade:

"""

Represents a facade for various computer parts.

"""

def __init__(self):

self.cpu = CPU()

self.memory = Memory()

self.ssd = SolidStateDrive()

def start(self):

self.cpu.freeze()

self.memory.load("0x00", self.ssd.read("100", "1024"))

self.cpu.jump("0x00")

self.cpu.execute()

def main():

"""

>>> computer_facade = ComputerFacade()

>>> computer_facade.start()

Freezing processor.

Loading from 0x00 data: 'Some data from sector 100 with size 1024'.

Jumping to: 0x00

Executing.

"""

if __name__ == "__main__":

import doctest

doctest.testmod(optionflags=doctest.ELLIPSIS)