Python 中的私有变量和方法

发布于 2024-09-12 05:56:59 字数 85 浏览 10 评论 0原文

什么时候应该对 Python 中的私有成员和方法使用 _foo （下划线）或 __bar （双下划线）？

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夜灵血窟げ 2024-09-19 05:56:59

请注意，Python 中不存在“私有方法”之类的东西。双下划线只是名称修饰：

>>> class A(object):
...     def __foo(self):
...         pass
... 
>>> a = A()
>>> A.__dict__.keys()
['__dict__', '_A__foo', '__module__', '__weakref__', '__doc__']
>>> a._A__foo()

因此，当您需要进行修饰时，__ 前缀非常有用，例如，为了不与继承链上方或下方的名称发生冲突。对于其他用途，单下划线会更好，恕我直言。

编辑，关于 __ 上的混淆，PEP-8 对此非常明确：

如果您的类打算进行子类化，并且您有属性
如果您不希望子类使用，请考虑将它们命名为
双前导下划线且无尾随下划线。这会调用
Python的名称修饰算法，其中类的名称是
损坏到属性名称中。这有助于避免属性名称
子类无意中包含以下属性时会发生冲突
同名。
注 3：并不是每个人都喜欢名称修改。尝试平衡
需要避免与潜在使用的意外名称冲突
高级调用者。

因此，如果您不希望子类意外地重新定义具有相同名称的自己的方法，请不要使用它。

Please note that there is no such thing as "private method" in Python. Double underscore is just name mangling:

>>> class A(object):
...     def __foo(self):
...         pass
... 
>>> a = A()
>>> A.__dict__.keys()
['__dict__', '_A__foo', '__module__', '__weakref__', '__doc__']
>>> a._A__foo()

So therefore __ prefix is useful when you need the mangling to occur, for example to not clash with names up or below inheritance chain. For other uses, single underscore would be better, IMHO.

EDIT, regarding confusion on __, PEP-8 is quite clear on that:

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

So if you don't expect subclass to accidentally re-define own method with same name, don't use it.

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如梦初醒的夏天 2024-09-19 05:56:59

双下划线。它以这样的方式破坏名称，以至于无法从类外部简单地通过 __fieldName 访问它，如果它们是私有的，这就是您想要开始的。（尽管访问该字段仍然不是很难。）

class Foo:
    def __init__(self):
        self.__privateField = 4;
        print self.__privateField # yields 4 no problem

foo = Foo()
foo.__privateField
# AttributeError: Foo instance has no attribute '__privateField'

可以通过 _Foo__privateField 来访问它。但它尖叫着“我是私人的，别碰我”，这比什么都没有好。

The double underscore. It mangles the name in such a way that it can't be accessed simply through __fieldName from outside the class, which is what you want to begin with if they're to be private. (Though it's still not very hard to access the field.)

class Foo:
    def __init__(self):
        self.__privateField = 4;
        print self.__privateField # yields 4 no problem

foo = Foo()
foo.__privateField
# AttributeError: Foo instance has no attribute '__privateField'

It will be accessible through _Foo__privateField instead. But it screams "I'M PRIVATE DON'T TOUCH ME", which is better than nothing.

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