Facade em Python
O Facade é um padrão de projeto estrutural que fornece uma interface simplificada (mas limitada) para um sistema complexo de classes, biblioteca, ou framework.
Embora o Facade diminua a complexidade geral do aplicativo, também ajuda a mover dependências indesejadas para um só local.
Complexidade:
Popularidade:
Exemplos de uso: O padrão Facade é comumente usado em aplicações escritas em Python. É especialmente útil ao trabalhar com bibliotecas e APIs complexas.
Identificação: O Facade pode ser reconhecido em uma classe que possui uma interface simples, mas delega a maior parte do trabalho para outras classes. Geralmente, as fachadas gerenciam o ciclo de vida completo dos objetos que usam.
Exemplo conceitual
Este exemplo ilustra a estrutura do padrão de projeto Facade. Ele se concentra em responder a estas perguntas:
- De quais classes ele consiste?
- Quais papéis essas classes desempenham?
- De que maneira os elementos do padrão estão relacionados?
main.py: Exemplo conceitual
from __future__ import annotations
class Facade:
"""
The Facade class provides a simple interface to the complex logic of one or
several subsystems. The Facade delegates the client requests to the
appropriate objects within the subsystem. The Facade is also responsible for
managing their lifecycle. All of this shields the client from the undesired
complexity of the subsystem.
"""
def __init__(self, subsystem1: Subsystem1, subsystem2: Subsystem2) -> None:
"""
Depending on your application's needs, you can provide the Facade with
existing subsystem objects or force the Facade to create them on its
own.
"""
self._subsystem1 = subsystem1 or Subsystem1()
self._subsystem2 = subsystem2 or Subsystem2()
def operation(self) -> str:
"""
The Facade's methods are convenient shortcuts to the sophisticated
functionality of the subsystems. However, clients get only to a fraction
of a subsystem's capabilities.
"""
results = []
results.append("Facade initializes subsystems:")
results.append(self._subsystem1.operation1())
results.append(self._subsystem2.operation1())
results.append("Facade orders subsystems to perform the action:")
results.append(self._subsystem1.operation_n())
results.append(self._subsystem2.operation_z())
return "\n".join(results)
class Subsystem1:
"""
The Subsystem can accept requests either from the facade or client directly.
In any case, to the Subsystem, the Facade is yet another client, and it's
not a part of the Subsystem.
"""
def operation1(self) -> str:
return "Subsystem1: Ready!"
# ...
def operation_n(self) -> str:
return "Subsystem1: Go!"
class Subsystem2:
"""
Some facades can work with multiple subsystems at the same time.
"""
def operation1(self) -> str:
return "Subsystem2: Get ready!"
# ...
def operation_z(self) -> str:
return "Subsystem2: Fire!"
def client_code(facade: Facade) -> None:
"""
The client code works with complex subsystems through a simple interface
provided by the Facade. When a facade manages the lifecycle of the
subsystem, the client might not even know about the existence of the
subsystem. This approach lets you keep the complexity under control.
"""
print(facade.operation(), end="")
if __name__ == "__main__":
# The client code may have some of the subsystem's objects already created.
# In this case, it might be worthwhile to initialize the Facade with these
# objects instead of letting the Facade create new instances.
subsystem1 = Subsystem1()
subsystem2 = Subsystem2()
facade = Facade(subsystem1, subsystem2)
client_code(facade)
Output.txt: Resultados da execução
Facade initializes subsystems:
Subsystem1: Ready!
Subsystem2: Get ready!
Facade orders subsystems to perform the action:
Subsystem1: Go!
Subsystem2: Fire!
