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Technique for accessing __var names.

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# Accessor function for private variables in Py3.x

def get_private_attr(inst, attr):
    'Access private variables without resorting to name mangling'
    s = ('class %(cls)s: \n' +
         ' def _show(self):  return self.%(attr)s \n' +
         'private = %(cls)s._show(inst) \n')
    s %= dict(cls=inst.__class__.__name__, attr=attr)
    d = dict(inst=inst)
    exec(s, d, d)
    return d['private']


if __name__ == '__main__':

    class MyClass:
        def __init__(self, x):
            self.__hidden = x

    m = MyClass(10)
    print(get_private_attr(m, '__hidden'))

Usually, private names are private for a reason. But, if you must get to them, here's a portable technique that doesn't rely on name mangling.

1 comment

Gabriel Genellina 12 years, 3 months ago  # | flag

Unfortunately it doesn't work when the attribute is declared in a base class.

class MyDerived(MyClass): pass

m = MyDerived(10)
print(get_private_attr(m, '__hidden'))

Traceback (most recent call last):
...
AttributeError: 'MyDerived' object has no attribute '_MyDerived__hidden'
Created by Raymond Hettinger on Tue, 3 Mar 2009 (MIT)
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