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Python 外观模式讲解和代码示例

外观是一种结构型设计模式 能为复杂系统 程序库或框架提供一个简单 但有限 的接口

尽管外观模式降低了程序的整体复杂度 但它同时也有助于将不需要的依赖移动到同一个位置



使用示例 使用 Python 开发的程序中会经常使用外观模式 它在与复杂程序库和 API 协作时特别有用

识别方法 外观可以通过使用简单接口 但将绝大部分工作委派给其他类的类来识别 通常情况下 外观管理其所使用的对象的完整生命周期



  • 它由哪些类组成
  • 这些类扮演了哪些角色
  • 模式中的各个元素会以何种方式相互关联

main.py: 概念示例

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

        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("Facade orders subsystems to perform the action:")
        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)

Output.txt: 执行结果

Facade initializes subsystems:
Subsystem1: Ready!
Subsystem2: Get ready!
Facade orders subsystems to perform the action:
Subsystem1: Go!
Subsystem2: Fire!


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