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Re: Unable to access module attribute with underscores in class method, Python 3

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  Re: Unable to access module attribute with underscores in class method, Python 3 Joseph Fox-Rabinovitz <jfoxrabinovitz@gmail.com> - 2016-01-07 12:33 -0500

#101369 — Re: Unable to access module attribute with underscores in class method, Python 3

> On Thu, Jan 7, 2016 at 11:14 AM, Joseph Fox-Rabinovitz <jfoxrabinovitz@gmail.com> wrote:
>
> Hi,
>
> I have a module attribute whose name starts with a pair of underscores. I am apparently unable to access it directly in a class method (within the same module, but that is not relevant as far as I can tell). The following bit of code illustrates the situation:
>
> __a = 3
> class B:
>     def __init__(self):
>         global __a
>         self.a = __a
> b = B()
>
> This results in a NameError because of name-mangling, despite the global declaration:
>
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "<stdin>", line 4, in __init__
> NameError: name '_B__a' is not defined
>
> Not using global does not make a difference. I posted a similar question on Stack Overflow, where the only reasonable answer given was to wrap __a in a container whose name is not mangled. For example, doing `self.a = globals()['__a']` or manually creating a dictionary with a non-mangled name and accessing that.
>
> I feel that there should be some way of accessing __a within the class directly in Python 3. Clearly my expectation that global would fix the issue is incorrect. I would appreciate either a solution or an explanation of what is going on that would convince me that accessing a module attribute in such a way should be forbidden.
>
>     -Joseph Fox-Rabinovitz
>
> P.S. For reference, the Stack Overflow question is here: http://stackoverflow.com/questions/34621484/how-to-access-private-variable-of-python-module-from-class

One more detail that makes me think that name mangling may be getting
greedy to the point of bugginess:

__a = 3
class B:
    def __init__(self):
        m = sys.modules[__name__]
        self.a = m.__a
b = B()

Raises the same exception as all the other way I tried to access __a:
'module' object has no attribute '_B__a'!

   -Joseph

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