blocks|key|2784771|text|更新：一开始，我并没有真正回答这个问题，但根据线索，我在最后找到了真正的答案，所以请耐心阅读到最后。简而言之，mangling适用于类中出现的所有名称。|type|unstyled|depth|inlineStyleRanges|offset|length|style|BOLD|entityRanges|data|2784772|Python类不能具有真正的私有属性，前缀__用于private。|CODE|2784773|我看到了下面的建议：|2784774|2784775|，但尽量避免使用__private的形式。我从来不用它。请相信我。如果你使用它，你和以后会后悔的。|blockquote|2784776|2784777|2784778|和：|2784779|2784780|+Forms+__private只是触发了一个新的private+name+mangling，它的目的是防止在子类中发生意外的命名空间冲突：MyClass.__private就变成了MyClass._MyClass__private。|2784781|2784782|2784783|Code+Like+a+Pythonista:+Idiomatic+Python-naming|2784784|我看了一下private+name+mangling，根据它，在班上所有的names都可以使用mangling：|2784785|2784786|+私有名称损坏：当一个在类定义中以文本形式出现的标识符名称以两个或更多下划线字符开头，而不是以两个或更多下划线结束时，它被认为是该类的私有名称。|2784787|2784788|2784789|因此，似乎所有出现在class.That中的名称都会被损坏，这就是为什么所有双下划线变量在类方法中都被损坏的原因。|2784790|entityMap|0|LINK|mutability|MUTABLE|url|https://web.archive.org/web/20180411011411/http://docs.python.org/dev/reference/expressions.html#atom-identifiers|1|https://web.archive.org/web/20180411011411/http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#naming|2^0|0|2|1E|Q|0|L|2|P|7|0|0|0|8|9|16|7|0|0|0|0|2|0|0|0|39|7|9|1Y|H|2J|P|P|L|0|0|0|0|0|1B|0|1B|1|0|0|1K|11|5|5|L|2|0|0|1|1Z|0|0|0|0|1L|0^^$0|@$1|2|3|4|5|6|7|1J|8|@$9|1K|A|1L|B|C]|$9|1M|A|1N|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|1O|8|@$9|1P|A|1Q|B|H]|$9|1R|A|1S|B|H]]|D|@]|E|$]]|$1|I|3|J|5|6|7|1T|8|@]|D|@]|E|$]]|$1|K|3|-4|5|6|7|1U|8|@]|D|@]|E|$]]|$1|L|3|M|5|N|7|1V|8|@$9|1W|A|1X|B|H]|$9|1Y|A|1Z|B|C]]|D|@]|E|$]]|$1|O|3|-4|5|6|7|20|8|@]|D|@]|E|$]]|$1|P|3|-4|5|6|7|21|8|@]|D|@]|E|$]]|$1|Q|3|R|5|6|7|22|8|@$9|23|A|24|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|25|8|@]|D|@]|E|$]]|$1|T|3|U|5|N|7|26|8|@$9|27|A|28|B|C]|$9|29|A|2A|B|H]|$9|2B|A|2C|B|H]|$9|2D|A|2E|B|H]]|D|@$9|2F|A|2G|1|2H]]|E|$]]|$1|V|3|-4|5|6|7|2I|8|@]|D|@]|E|$]]|$1|W|3|-4|5|6|7|2J|8|@]|D|@]|E|$]]|$1|X|3|Y|5|6|7|2K|8|@$9|2L|A|2M|B|C]]|D|@$9|2N|A|2O|1|2P]]|E|$]]|$1|Z|3|10|5|6|7|2Q|8|@$9|2R|A|2S|B|C]|$9|2T|A|2U|B|H]]|D|@$9|2V|A|2W|1|2X]]|E|$]]|$1|11|3|-4|5|6|7|2Y|8|@]|D|@]|E|$]]|$1|12|3|13|5|N|7|2Z|8|@$9|30|A|31|B|C]]|D|@]|E|$]]|$1|14|3|-4|5|6|7|32|8|@]|D|@]|E|$]]|$1|15|3|-4|5|6|7|33|8|@]|D|@]|E|$]]|$1|16|3|17|5|6|7|34|8|@$9|35|A|36|B|C]]|D|@]|E|$]]|$1|18|3|-4|5|6|7|37|8|@]|D|@]|E|$]]]|19|$1A|$5|1B|1C|1D|E|$1E|1F]]|1G|$5|1B|1C|1D|E|$1E|1H]]|1I|$5|1B|1C|1D|E|$1E|1F]]]]

Update: at first, I didn't really answer the question, but according to the clues, I found the real answer at the end, so please be patient and read until the end. In short, mangling is for all the names that appear in the class.

Python class can not have real private attribute, prefix <code>__</code> is for <code>private</code> purpose.

I have seen the below suggestion:

<blockquote>
 But try to avoid the <code>__private</code> form. I never use it. Trust me. If you use it, you WILL regret it later.
</blockquote>

and:

<blockquote>
 Forms <code>__private</code> just trigger a <a href="https://web.archive.org/web/20180411011411/http://docs.python.org/dev/reference/expressions.html#atom-identifiers" rel="nofollow noreferrer">private name mangling</a> whose purpose is to prevent accidental namespace collisions in subclasses: <code>MyClass.__private</code> just becomes <code>MyClass._MyClass__private</code>.
</blockquote>

<a href="https://web.archive.org/web/20180411011411/http://python.net/~goodger/projects/pycon/2007/idiomatic/handout.html#naming" rel="nofollow noreferrer">Code Like a Pythonista: Idiomatic Python-naming</a>

I looked <a href="https://web.archive.org/web/20180411011411/http://docs.python.org/dev/reference/expressions.html#atom-identifiers" rel="nofollow noreferrer">private name mangling</a> and according to it, mangling is for all <code>names</code> in class:

<blockquote>
 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.
</blockquote>

So, It seems that mangling is for all the names that appear in class.That is why all double-underscore variables are mangled in class methods.

blocks|key|70942|text|这不是一个疏忽。事实上，私有全局变量曾经专门在tutorial中做广告|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|70943|70944|现在对类私有标识符的支持有限。这种损坏是在不考虑标识符的语法位置的情况下完成的，因此它可以用于定义类私有的实例和类变量、方法、以及全局，甚至可以将这个类私有的实例变量存储在其他类的实例上。|blockquote|style|BOLD|70945|70946|70947|(我检查了提交历史记录，但original+commit不包括设计选择的理由。)我们可以推测它是为了实现像私有全局这样的东西，但我们也可以推测以这种方式实现它是最容易的，如果其他选择更容易的话，实现者不会被私有全局的前景所动摇。|70948|entityMap|0|LINK|mutability|MUTABLE|url|https://docs.python.org/release/1.5/tut/node67.html#SECTION0010600000000000000000|1|https://github.com/python/cpython/commit/8ff077b0949791c6b699cb179749d929a9fdc98a^0|N|8|0|0|0|1R|4|0|0|0|D|F|1|0^^$0|@$1|2|3|4|5|6|7|X|8|@]|9|@$A|Y|B|Z|1|10]]|C|$]]|$1|D|3|-4|5|6|7|11|8|@]|9|@]|C|$]]|$1|E|3|F|5|G|7|12|8|@$A|13|B|14|H|I]]|9|@]|C|$]]|$1|J|3|-4|5|6|7|15|8|@]|9|@]|C|$]]|$1|K|3|-4|5|6|7|16|8|@]|9|@]|C|$]]|$1|L|3|M|5|6|7|17|8|@]|9|@$A|18|B|19|1|1A]]|C|$]]|$1|N|3|-4|5|6|7|1B|8|@]|9|@]|C|$]]]|O|$P|$5|Q|R|S|C|$T|U]]|V|$5|Q|R|S|C|$T|W]]]]

This was not an oversight. In fact, private globals used to be specifically advertised in the <a href="https://docs.python.org/release/1.5/tut/node67.html#SECTION0010600000000000000000" rel="nofollow noreferrer">tutorial</a>:

<blockquote>
 There is now limited support for class-private identifiers. Any identifier of the form <code>__spam</code> (at least two leading underscores, at most one trailing underscore) is now textually replaced with <code>_classname__spam</code>, where <code>classname</code> is the current class name with leading underscore(s) stripped. This mangling is done without regard of the syntactic position of the identifier, so it can be used to define class-private instance and class variables, methods, as well as globals, and even to store instance variables private to this class on instances of other classes.
</blockquote>

Without specific references, like a mailing list conversation or something, we can only speculate as to why it was designed this way. (I checked the commit history, but the <a href="https://github.com/python/cpython/commit/8ff077b0949791c6b699cb179749d929a9fdc98a" rel="nofollow noreferrer">original commit</a> includes no justification for design choices.) We can speculate that it was to enable things like private globals, but we can also speculate that it was just easiest to implement it this way and that the implementers wouldn't have been swayed by the prospect of private globals if other options were easier. It would certainly have been a lot harder to implement name mangling in a way that only affected the class's instance and class attributes.

Edit: Both current answers talk about the fact that there is mangling inside classes. My question is about values inside class methods - note that the parsing in the method scope is different from the class scope, or <code>__CLASS</code> would be printable.

<hr>

This seems to be the case in python 2.7 and 3.6.

For example, this code

<pre><code>__GLOBAL = 'global'
_Bar__MANGLED_GLOBAL = 'mangled global'

class Bar(object):
 __CLASS = 'class'

 def baz(self):
 __LOCAL = 'local'
 try:
 print __LOCAL
 except Exception as e:
 print e
 try:
 print __CLASS
 except Exception as e:
 print e
 try:
 print __GLOBAL
 except Exception as e:
 print e
 try:
 print __MANGLED_GLOBAL
 except Exception as e:
 print e

Bar().baz()
</code></pre>

Will give

<pre><code>local
global name '_Bar__CLASS' is not defined
global name '_Bar__GLOBAL' is not defined
mangled global
</code></pre>

I understand the logic when there is an <code>other.__x</code>, or needing a class-level <code>__foo</code> to equate to <code>self.__foo</code>, but this seems like an oversight, where anything inside the class scope is automatically rewritten.

Why are all double-underscore variables mangled in class methods

Python

编辑:目前的两个答案都谈到了类内部存在混乱的事实。我的问题是关于类方法中的值-请注意，方法作用域中的解析不同于类作用域，否则__CLASS将是可打印的。在Python2.7和3.6中似乎就是这种情况。例如，下面的代码__GLOBAL = 'global'_Bar__MANGLED_GLOBAL = 'mangled g...

问为什么类方法中所有的双下划线变量都是乱码？
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问为什么类方法中所有的双下划线变量都是乱码？
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