我知道，Python 中没有“真正的”私有(private)/ protected 方法。这种方法并不是要隐藏任何东西。我只是想了解 Python 是做什么的。

class Parent(object):
    def _protected(self):
        pass

    def __private(self):
        pass

class Child(Parent):
    def foo(self):
        self._protected()   # This works

    def bar(self):
        self.__private()    # This doesn't work, I get a AttributeError:
                            # 'Child' object has no attribute '_Child__private'

那么，这种行为是否意味着“ protected ”方法将被继承而“私有(private)”方法根本不会被继承？
还是我错过了什么？

最佳答案

Python 没有隐私模型，没有像 C++、C# 或 Java 那样的访问修饰符。没有真正的“ protected ”或“私有(private)”属性。

带有前导双下划线且没有尾随双下划线的名称被重整以保护它们在继承时不会发生冲突。子类可以定义自己的 __private() 方法，这些方法不会干扰父类的同名。此类名称被视为类私有(private)；它们仍然可以从类外访问，但发生意外冲突的可能性要小得多。

Mangling 是通过在任何此类名称前面加上一个额外的下划线和类名来完成的(无论名称如何使用或是否存在)，从而有效地为它们提供一个 命名空间。在 Parent 类中，任何 __private 标识符(在编译时)被名称 _Parent__private 替换，而在 Child 中code> 类的标识符被替换为 _Child__private，在类定义中的任何位置。

以下将起作用:

class Child(Parent):
    def foo(self):
        self._protected()

    def bar(self):
        self._Parent__private()

见 Reserved classes of identifiers在词法分析文档中:

__*
Class-private names. Names in this category, when used within the context of a class definition, are re-written to use a mangled form to help avoid name clashes between “private” attributes of base and derived classes.

和引用的documentation on names :

Private name mangling: When an identifier that textually occurs in a class definition begins with two or more underscore characters and does not end in two or more underscores, it is considered a private name of that class. Private names are transformed to a longer form before code is generated for them. The transformation inserts the class name, with leading underscores removed and a single underscore inserted, in front of the name. For example, the identifier __spam occurring in a class named Ham will be transformed to _Ham__spam. This transformation is independent of the syntactical context in which the identifier is used.

不要使用类私有(private)名称，除非您特别希望避免告诉开发人员想要子类化您的类他们不能使用某些名称或冒着破坏您的类的风险。在已发布的框架和库之外，此功能几乎没有用处。

PEP 8 Python Style Guide对私有(private)名称修改有这样的说法:

If your class is intended to be subclassed, and you have attributes that you do not want subclasses to use, consider naming them with double leading underscores and no trailing underscores. This invokes Python's name mangling algorithm, where the name of the class is mangled into the attribute name. This helps avoid attribute name collisions should subclasses inadvertently contain attributes with the same name.

Note 1: Note that only the simple class name is used in the mangled name, so if a subclass chooses both the same class name and attribute name, you can still get name collisions.

Note 2: Name mangling can make certain uses, such as debugging and __getattr__(), less convenient. However the name mangling algorithm is well documented and easy to perform manually.

Note 3: Not everyone likes name mangling. Try to balance the need to avoid accidental name clashes with potential use by advanced callers.

关于python - Python中私有(private)和 protected 方法的继承，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/20261517/