[Python-projects] pylint W0212 - Access to a protected member of a client class

[Sylvain Thénault]

On Wednesday 08 November à 19:01, duncan.gibson at xs4all.nl wrote:
> 
> pylint --version gives:
> ----------------------------------------------------------------------
> 
> pylint 0.12.1, astng 0.16.1, common 0.19.2
> Python 2.5 (r25:51908, Oct 11 2006, 16:04:20) 
> [GCC 3.4.6]
> 
> 
> If I run the following example Python script:
> ----------------------------------------------------------------------
> 
> #!/usr/bin/env python
> ''' example program to ask about pylint message W0212 '''
> 
> class Thing(object):
>     ''' example class '''
> 
>     _next_id = 0
> 
>     __slots__ = ('number', 'name')
> 
>     def __init__(self, name):
>         self.number = Thing.next_id()
>         self.name   = name
> 
>     def __str__(self):
>         return '(number=%d, name="%s")' % (self.number, self.name)
> 
>     def next_id():
>         ''' static method to increment "private" class attribute '''
>         Thing._next_id += 1
>         return Thing._next_id
>     next_id = staticmethod(next_id)
> 
>     def reset_id():
>         ''' static method to reset "private" class attribute '''
>         Thing._next_id = 0
>     reset_id = staticmethod(reset_id)
> 
> 
> if __name__ == '__main__':
> 
>     XX = Thing('one')
>     print 'XX =', XX
>     YY = Thing('two')
>     print 'YY =', YY
> 
>     Thing.reset_id()
>     ZZ = Thing('ten')
>     print 'ZZ =', ZZ
> 
> 
> then I get the following output, as expected:
> ----------------------------------------------------------------------
>     
> XX = (number=1, name="one")
> YY = (number=2, name="two")
> ZZ = (number=1, name="ten")
> 
> 
> If I then run pylint on the script, I get two W0212 messages:
> ----------------------------------------------------------------------
> 
> W: 20:Thing.next_id: Access to a protected member _next_id of a client class
> W: 21:Thing.next_id: Access to a protected member _next_id of a client class
> 
> 
> So I ran pylint --help-message=W0212 to check the warning:
> ----------------------------------------------------------------------
> 
> :W0212: *Access to a protected member %s of a client class*
>   Used when a protected member (i.e. class member with a name beginning with an
>   underscore) is access outside the class or a descendant of the class where
>   it's defined. This message belongs to the classes checker.
> 
> 
> In my original code, I was accessing the "private" class attribute
> directly from outside the class, received W0212 messages, and to avoid
> the warnings I encapsulated the access in "public" static methods like
> those above, and *still* got the warning messages.
> 
> And now that I've typed in all of this text, I realise that pylint gives
> the warnings for accessing the private _next_id class attribute in the
> next_id() static method, but not for accessing it in the reset_id() method!
> 
> What is the expected behaviour? Should both give warnings, or neither?

The warning is not printed into reset_id since there's only an assigment 
there, no access. I'm not sure we would like a warning even if we are
actually outside the class. Opinion someone ? Secondly I would have
expected 'as you did that your encpsulation fix the warning. This is a
bug, I've added it to the tracker.
 
> PS. It's not too important, but all of the "To many ..." warning messages
>     should really read "Too many..." with two Os.
>     English is tough stuff http://alt-usage-english.org/excerpts/fxenglis.html

those are already fixed in the repository.
-- 
Sylvain Thénault                               LOGILAB, Paris (France)
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