在Python 3中练习继承时引发错误

Question

当我执行时，它抛出错误：

 ....
  ......
    class Dog(Pet):
  File "D:\untitled2\Pet.py", line 13, in Dog
    Dog.numberoflegs = 4
NameError: name 'Dog' is not defined
Fish.numberoflegs = 0
NameError: name 'Fish' is not defined

请帮忙

class Pet:
    numberoflegs = 0
    def sleep(self,name):
        print("the {} sleeps".format(name))
    def countlegs(self):
        print("I have {} legs".format(self.numberoflegs))


#type = input("enter pet type")
#dog.sleep(type)

class Dog(Pet):
    Dog.numberoflegs = 4
    def bark(self):
        print ("the dog sounds woof")

class Fish(Pet):
    Fish.numberoflegs = 0


kuta = Dog()
kuta.countlegs()
kuta.bark()
machi = Fish()
machi.countlegs()

Answer 1

类属性只是添加到类中，而不是以类名作为前缀：

class Dog(Pet):
    numberoflegs = 4
    # etc

class Fish(Pet):
    numberoflegs = 0

您可以使用Dog.numberoflegs = 3更改它（如果默认情况下您有三条腿的狗）

类属性在所有实例之间共享

看

• What is the difference between class and instance attributes?
• https://www.python.org/dev/peps/pep-0008/对于一些样式提示，您的命名约定与建议的有很大不同