Question

这是一段学习继承的Python代码。

class Animal():
    __name= None
    __sound = None

    def __init__(self, name , sound):
        self.__name= name
        self.__sound = sound 
    def ToString(self):
        print ("The {} has the sound  {}".format(self.__name ,
                                                self.__sound))


cat = Animal('Tiger' , 'roars')
cat.ToString()


class Panther(Animal):
    __owner = None

    def __init__(self , name ,sound ,owner):
        self.__owner = owner
        super(Panther ,self).__init__(name, sound)
    def ToString(self):
        print(self.__owner)
        print(self.__name) 

leopard = Panther('Leopard' , 'roars' , 'Senegal')
leopard.ToString()

但是当我尝试在Pycharm中运行它时，我收到以下错误：

/Library/Frameworks/Python.framework/Versions/3.5/bin/python3.5   /Users/venkat/PycharmProjects/PythonOneVideo/main.py老虎有   声音咆哮Senegal Traceback（最近的呼叫最后一次）：文件   “/Users/venkat/PycharmProjects/PythonOneVideo/main.py”，第41行，in          leopard.ToString（）文件“/Users/venkat/PycharmProjects/PythonOneVideo/main.py”，第35行，in   的ToString       print（self .__ name）AttributeError：'Panther'对象没有属性'_Panther__name'

使用退出代码1完成处理

调用超类构造函数有什么问题？为什么会出现此错误以及如何解决此问题？任何帮助将不胜感激。

Answer 1

几个问题：

py {3 super的语法：super().__init__(name, sound)
name mangling：以__开头的实例变量（两个下划线）将为它们添加_ClassName。子课程将无法以通常的方式访问它们。
ToString：为什么不__str__（不要在__str__内打印;只返回str）？
什么是类变量（_name等）？为什么不把它们作为实例变量（self._name）？

这辆工程巴士不完整......

class Animal():
    # _name= None
    # _sound = None

    def __init__(self, name , sound):
        self._name= name
        self._sound = sound

#    def ToString(self):
#        print ("The {} has the sound  {}".format(self._name ,
#                                                self._sound))

    def __str__(self):
        fmt = 'The {self._name} has the sound {self._sound}'
        return fmt.format(self=self)

cat = Animal('Tiger' , 'roars')
print(cat)

class Panther(Animal):
    # _owner = None

    def __init__(self , name ,sound ,owner):
        self.__owner = owner
        super().__init__(name, sound)

#    def ToString(self):
#        # print(self._owner)
#        print(self._name)

leopard = Panther('Leopard' , 'roars' , 'Senegal')
print(leopard)

Answer 2

从属性中删除两个前导下划线：

class Animal():
    name= None
    sound = None

    def __init__(self, name , sound):
        self.name= name
        self.sound = sound 
    def ToString(self):
        print ("The {} has the sound  {}".format(self.name ,
                                                self.sound))


cat = Animal('Tiger' , 'roars')
cat.ToString()


class Panther(Animal):
    owner = None

    def __init__(self , name ,sound ,owner):
        self.owner = owner
        super(Panther ,self).__init__(name, sound)
    def ToString(self):
        print(self.owner)
        print(self.name) 

leopard = Panther('Leopard' , 'roars' , 'Senegal')
leopard.ToString()

输出：

The Tiger has the sound  roars
Senegal
Leopard

两个主要下划线使您的属性＆＃34;私有＆＃34;。这是我name mangling完成的，即在所有属性前面添加_ClassName和两个前导下划线。这可以防止你继续工作。

Answer 3

您的错误源于Python在__前添加变量名时执行的名称修改。如果你只使用没有双尾下划线的名称，这可以正常工作：

class Animal():
    def __init__(self, name , sound):
        self._name= name
        self._sound = sound 
    def ToString(self):
        print ("The {} has the sound  {}".format(self._name ,
                                                self._sound))


cat = Animal('Tiger' , 'roars')
cat.ToString()


class Panther(Animal):

    def __init__(self , name ,sound ,owner):
        self._owner = owner
        super(Panther ,self).__init__(name, sound)
    def ToString(self):
        print(self._owner)
        print(self._name)

并打印出来：

>>> leopard = Panther('Leopard' , 'roars' , 'Senegal')
>>> leopard.ToString()
The Tiger has the sound  roars
Senegal
Leopard

在Python 3.5中使用super（）时的属性错误

3 个答案: