python---抽象方法的简易使用

#通过子类实例父类
from abc import ABC,abstractmethod,abstractproperty

class Drawable(ABC):
    @abstractproperty
    def  size(self):
        pass
    @abstractmethod
    def  draw(self,x,y,scale=1.0):
        pass
    def double_draw(self,x,y):
        self.draw(x,y,scale=2.0)


class Circle(Drawable):
    def draw(self, x, y, scale=1.0):
        print(x*scale,y*scale)
    @property
    def size(self):
        return 'Circle size'

c=Circle()
print(dir(c))
c.draw(1,2)
c.double_draw(1,2)

----
#output:

['__abstractmethods__', '__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '__weakref__', '_abc_impl', 'double_draw', 'draw', 'size']
1.0 2.0
2.0 4.0

----

#父类不能直接实例调用
class Drawable(ABC):
    @abstractproperty
    def  size(self):
        pass
    @abstractmethod
    def  draw(self,x,y,scale=1.0):
        pass
    def double_draw(self,x,y):
        self.draw(x,y,scale=2.0)


class Circle(Drawable):
    def draw(self, x, y, scale=1.0):
        print(x*scale,y*scale)
    @property
    def size(self):
        return 'Circle size'

b=Drawable()
b.draw(1,2)


----
#output:

Traceback (most recent call last):
File "D:/djangocode/Celery_ttoia/app/tests.py", line 50, in <module>
b=Drawable()
TypeError: Can't instantiate abstract class Drawable with abstract methods draw, size

----

抽象方法是父类的一个方法, 父类没有实现这个方法, 父类是不可以实例化的. 子类继承父类, 子类必须实现父类定义的抽象方法, 子类才可以被实例化. Python中的abc提供了@abstractmethod装饰器实现抽象方法的定义

from abc import ABC, abstractmethod

class Foo(ABC):
    @abstractmethod
    def fun(self):
        """
        你需要在子类中实现该方法, 子类才允许被实例化
        """

class SubFoo(Foo):

    def fun(self):
        print("子类实现父类的抽象方法")
    def go(self):
        print(666)

if __name__ == "__main__":

    sf = SubFoo()
    sf.fun()
  ----
#outout:
子类实现父类的抽象方法

当子类未重写父类fun方法时：

from abc import ABC, abstractmethod

class Foo(ABC):
    @abstractmethod
    def fun(self):
        """
        你需要在子类中实现该方法, 子类才允许被实例化
        """

class SubFoo(Foo):

    # def fun(self):
        # print("子类实现父类的抽象方法")
    def go(self):
        print(666)

if __name__ == "__main__":

    sf = SubFoo()
    sf.go()
----
#output：
Traceback (most recent call last):
  File "D:/djangocode/Celery_ttoia/app/tests.py", line 122, in <module>
    sf = SubFoo()
TypeError: Can't instantiate abstract class SubFoo with abstract methods fun
----