[code-quality] __all__ defined inside a class

[Alexander Todorov]

Hi folks,
I've just noticed that a legacy piece of code I'm working with contains the 
following pattern:

class SomeClass(object):
     __all__ = ['add', 'delete']

     def __init__(self):
         pass

     def get(self):
         pass

     def add(self, x):
         pass

     def delete(self, x):
         pass


And the caller of this class actually uses the .get() method. I have this in at 
least 10 different places.

I wasn't able to find any information about __all__ having any special meaning 
when defined inside a class so this looks like a mistake.

Q1: Do we want pylint to warn about __all__ being detected not at module level ?

Q2: Do we want another check to warn about class attributes staring with 
single/double underscore ?

--
Alex