How to access private variable of Python module from class

Question

In Python 3, prefixing a class variable makes it private by mangling the name within the class. How do I access a module variable within a class?

For example, the following two ways do not work:

__a = 3
class B:
    def __init__(self):
        self.a = __a
b = B()

results in:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __init__
NameError: name '_B__a' is not defined

Using global does not help either:

__a = 3
class B:
    def __init__(self):
        global __a
        self.a = __a
b = B()

results in:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 4, in __init__
NameError: name '_B__a' is not defined

Running locals() shows that the variable __a exists unmangled:

>>> locals()
{'__package__': None, '__name__': '__main__',
 '__loader__': <class '_frozen_importlib.BuiltinImporter'>,
 '__doc__': None, '__a': 3, 'B': <class '__main__.B'>,
 '__builtins__': <module 'builtins' (built-in)>, '__spec__': None}

[Newlines added for legibility]

Running same code in a module (as opposed to interpreter) results in the exact same behavior. Using Anaconda's Python 3.5.1 :: Continuum Analytics, Inc..

Answer 1

It's ugly but You could access globals:

__a = 3
class B:
    def __init__(self):
        self.a = globals()["__a"]
b = B()

You can also put it in a dict:

__a = 3

d = {"__a": __a}

class B:
    def __init__(self):
        self.a = d["__a"]
b = B()

Or a list, tuple etc.. and index:

__a = 3

l = [__a]

class B:
    def __init__(self):
        self.a = l[0]
b = B()