在python中装饰基类方法答案

【问题标题】：decorating base class methods in python在python中装饰基类方法
【发布时间】：2021-07-18 09:25:37
【问题描述】：

我有一个python类，例如：

from abc import ABC, abstractmethod


class Drawing(ABC):

    @abstractmethod
    def draw(self):
        pass


class Sketch(Drawing):

    # overriding abstract method
    def draw(self):
        print("Drawing a sketch")



# Driver code
R = Sketch()
R.draw()

这是他想要达到的目标：

创建一个实现draw()接口的抽象绘图类。以 Sketch 类的形式开发 Drawing 类的子类。用 Sketchdraw 的消息让 draw() 接口更具体。

问题： 但我也想创建改变素描风格的装饰器（例如“铅笔素描”或“钢笔素描”）。我的问题是我怎样才能做到正确，我在下面的代码中所做的是否正确？

 class Drawing(ABC):

    @abstractmethod
    def draw(self):
        pass
    @abstractmethod
    def drawPencil(self):
        pass
    @abstractmethod
    def drawPen(self):
        pass

class Sketch(Drawing):
    
   
    def draw(self):
        print("Drawing a sketch")

    def drawPencil(self):
        print("Drawing with pencil")

    def drawPen(self):
        print("Drawing with pen")

【问题讨论】：

标签： python inheritance abstract-class decorator python-decorators

【解决方案1】：

我会作为基类

from abc import ABCMeta, abstractmethod

class IDrawing(metaclass=ABCMeta):
    
    @staticmethod
    @abstractmethod
    def draw():
        pass

class Sketch(IDrawing):
    #override
    def draw(self):
        print("Drawing a sketch")

r = Sketch()
r.draw()
#Drawing a sketch

如果此抽象方法不需要任何类实习生属性，则使用@staticmethod。否则，您使用 @classmethod 并作为第一个参数 cls （因为 abstractmethod 不能使用 self 来引用实例）。没有@staticmethod 也可以工作...

现在使用你的 print 函数，我会像这样定义装饰器：

from abc import ABCMeta, abstractmethod

class IDrawing(metaclass=ABCMeta):
    
    @staticmethod
    @abstractmethod
    def draw():
        pass

def pen(func):
    def new_func(*args, **kwargs):
        func(*args, **kwargs)
        print("with a pen")
    return new_func

def pencil(func):
    def new_func(*args, **kwargs):
        func(*args, **kwargs)
        print("with a pencil")
    return new_func

class Sketch(IDrawing):
    #override
    def draw(self):
        print("Drawing a sketch")
    
    @pen
    def drawPen(self):
        print("Drawing ", end="")
    
    @pencil
    def drawPencil(self):
        print("Drawing ", end="")

r = Sketch()
r.draw()
r.drawPen()
r.drawPencil()
#Drawing a sketch
#Drawing with a pen
#Drawing with a pencil

我个人更喜欢返回字符串并在调用它们时使用print 命令的函数。


from abc import ABCMeta, abstractmethod

class IDrawing(metaclass=ABCMeta):
    
    @staticmethod
    @abstractmethod
    def draw():
        pass

def pen(func):
    def new_func(*args, **kwargs):
        return func(*args, **kwargs) + " with a pen"
    return new_func

def pencil(func):
    def new_func(*args, **kwargs):
        return func(*args, **kwargs) + " with a pencil"
    return new_func

class Sketch(IDrawing):
    #override
    def draw(self):
        return "Drawing a sketch"
    
    @pen
    def drawPen(self):
        return "Drawing"
    
    @pencil
    def drawPencil(self):
        return "Drawing"

r = Sketch()
print(r.draw())
print(r.drawPen())
print(r.drawPencil())
#Drawing a sketch
#Drawing with a pen
#Drawing with a pencil

【讨论】：

【解决方案2】：

你的意思是你想要不同的派生类以不同的方式绘制？

from abc import ABC, abstractmethod

class Drawing(ABC):
    @abstractmethod
    def draw(self):
        pass

class Sketch(Drawing):
    def draw(self):
        print("Drawing a sketch")

class PencilSketch(Drawing):
    def draw(self):
        print("Drawing with pencil")

class PenSketch(Drawing):
    def draw(self):
        print("Drawing with pen")

drawObjs = [Sketch(), PencilSketch(), PenSketch()]
for obj in drawObjs:
    obj.draw()

输出：

Drawing a sketch
Drawing with pencil
Drawing with pen

【讨论】：