Python 装饰模式讲解和代码示例
装饰是一种结构设计模式， 允许你通过将对象放入特殊封装对象中来为原对象增加新的行为。
由于目标对象和装饰器遵循同一接口， 因此你可用装饰来对对象进行无限次的封装。 结果对象将获得所有封装器叠加而来的行为。
复杂度：
流行度：
使用示例： 装饰在 Python 代码中可谓是标准配置， 尤其是在与流式加载相关的代码中。
识别方法： 装饰可通过以当前类或对象为参数的创建方法或构造函数来识别。
概念示例
本例说明了装饰设计模式的结构并重点回答了下面的问题：
- 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
class Component():
"""
The base Component interface defines operations that can be altered by
decorators.
"""
def operation(self) -> str:
pass
class ConcreteComponent(Component):
"""
Concrete Components provide default implementations of the operations. There
might be several variations of these classes.
"""
def operation(self) -> str:
return "ConcreteComponent"
class Decorator(Component):
"""
The base Decorator class follows the same interface as the other components.
The primary purpose of this class is to define the wrapping interface for
all concrete decorators. The default implementation of the wrapping code
might include a field for storing a wrapped component and the means to
initialize it.
"""
_component: Component = None
def __init__(self, component: Component) -> None:
self._component = component
@property
def component(self) -> Component:
"""
The Decorator delegates all work to the wrapped component.
"""
return self._component
def operation(self) -> str:
return self._component.operation()
class ConcreteDecoratorA(Decorator):
"""
Concrete Decorators call the wrapped object and alter its result in some
way.
"""
def operation(self) -> str:
"""
Decorators may call parent implementation of the operation, instead of
calling the wrapped object directly. This approach simplifies extension
of decorator classes.
"""
return f"ConcreteDecoratorA({self.component.operation()})"
class ConcreteDecoratorB(Decorator):
"""
Decorators can execute their behavior either before or after the call to a
wrapped object.
"""
def operation(self) -> str:
return f"ConcreteDecoratorB({self.component.operation()})"
def client_code(component: Component) -> None:
"""
The client code works with all objects using the Component interface. This
way it can stay independent of the concrete classes of components it works
with.
"""
# ...
print(f"RESULT: {component.operation()}", end="")
# ...
if __name__ == "__main__":
# This way the client code can support both simple components...
simple = ConcreteComponent()
print("Client: I've got a simple component:")
client_code(simple)
print("\n")
# ...as well as decorated ones.
#
# Note how decorators can wrap not only simple components but the other
# decorators as well.
decorator1 = ConcreteDecoratorA(simple)
decorator2 = ConcreteDecoratorB(decorator1)
print("Client: Now I've got a decorated component:")
client_code(decorator2)
Output.txt: 执行结果
Client: I've got a simple component:
RESULT: ConcreteComponent
Client: Now I've got a decorated component:
RESULT: ConcreteDecoratorB(ConcreteDecoratorA(ConcreteComponent))
