Python的＆QUOT;私人和QU​​OT;名称重整和实例VS类属性 [英] Python "private" name mangling and instance vs class attributes

问题描述

我在写这需要访问私有变量，发现这种差异一个装饰。任何人都可以解释一下吗？

I was writing a decorator that needs to access private variables and found this discrepancy. Can anyone explain this?

（Python 2.5的）

(Python 2.5)

如预期中的类定义的属性命名重整作品：

Naming mangling works as expected for attributes defined in the class:

>>> class Tester(object):
...    __foo = "hi"

>>> t = Tester()
>>> t._Tester__foo
'hi'

实例属性不工作（这是我们应该做的是正确的方式？）

Instance attributes do not work (and this is the way we are supposed to do it right?)

>>> class Tester(object):
...     def __init__(self):
...         self.__foo = "hi"

>>> t = Tester()
>>> t._Tester__foo
AttributeError: 'Tester' object has no attribute '_Tester__foo'

P.S。是类属性，这些正确的字？他们不是静态的，但如果你把其中的一个列表，或其他一些可变类型，它是共享的...

P.S. Is "class attribute" the right word for these? They aren't static, but if you make one of those a list, or some other mutable type, it is shared...

更新

在事实上，第二个例子中工作得很好了。这是一个硬件问题（重新启动帮助）。

In fact, second example works fine, too. It was a hardware issue (restart helped).

推荐答案

这其实是不的正确。

名称重整发生在类的创建时间;引用错位的名称的任何职能调整为好。

Name mangling takes place at class creation time; any functions that refer to mangled names are adjusted as well.

我无法重现你的榜样，至少在Python版本2.4，2.5，2.6，3.1和3.2在Mac上：

I cannot reproduce your example, at least not in Python versions 2.4, 2.5, 2.6, 3.1 and 3.2 on the Mac:

>>> class Tester(object):
...     def __init__(self):
...         self.__foo = "hi"
... 
>>> Tester()._Tester__foo
'hi'
>>> Tester().__foo
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Tester' object has no attribute '__foo'

如果您拆卸功能字节code可以看到的名字已经错位，以及：

If you disassemble the function bytecode you can see the name has been mangled as well:

>>> import dis
>>> dis.dis(Tester.__init__)
  3           0 LOAD_CONST               1 ('hi')
              3 LOAD_FAST                0 (self)
              6 STORE_ATTR               1 (_Tester__foo)
              9 LOAD_CONST               0 (None)
             12 RETURN_VALUE        

我检查了编译器的源和所有名称是通过压榨机，自2002年以来一直保持同一个code路径至少运行。

I've checked the compiler source and all names are run through the mangler, a code path that has remained the same since 2002 at least.

是的，类属性和实例属性是正确的术语。类属性始终共享，但分配的到的上一个实例的属性分配给该实例。变异列表或其他可变对象是不一样的属性分配。

And yes, class attributes and instance attributes are the correct terms. Class attributes are always shared, but assignment to an attribute on an instance assigns to the instance. Mutating a list or other mutable objects is not the same as attribute assignment.

这篇关于Python的＆QUOT;私人和QU​​OT;名称重整和实例VS类属性的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！