Pylint false positives

[Terry Reedy]

On 8/14/2018 5:05 AM, Thomas Jollans wrote:
> On 2018-08-14 09:38, Frank Millman wrote:
>> Hi all
>>
>> Pylint is flagging a lot of lines as errors that I would consider to be
>> acceptable.
>>
>> I have an abstract class ClassA with a number of concrete sub-classes.
>> ClassA has a method which invokes 'self.method_b()' which is defined
>> separately on each sub-class. Pylint complains that "Instance of
>> 'ClassA' has no  'method_b' member".
>>
>> First question - as a matter of style, is Pylint correct? If so, I could
>> define 'method_b' in ClassA and raise NotImplementedError. Is this
>> considered more pythonic? The downside is that I have quite a few of
>> them, so it would add some clutter.

If I were reading you class, I would like to see all methods defined 
there.  If you went the old NotImplemented(Error) route, you could avoid 
cluttter with

     method_c = method_d = method_e = method_b

but I would also want docstrings.  At that point, I would consider 
abstractmethod.  But I have not used that, not seen an stdlib class that 
does.

> I wouldn't say it's unpythonic per se, but if your ClassA is logically
> an abstract base class that requires certain methods to be implemented
> in subclasses, then it's probably clearer to use Python's abc [1]
> facilities, and declare your abstract methods as actual abstractmethods.
> 
> [1]: https://docs.python.org/3/library/abc.html
> 
> i.e.
> 
> from abc import ABC, abstractmethod
> class ClassA(ABC):
>      def do_stuff(self):
>          return self.method_b(42)**3
> 
>      @abstractmethod
>      def method_b(self, answer):
>          """
>          This is a great place to put a docstring
>          """
> 
> You *can* raise NotImplementedError in your abstractmethods, but I don't
> think it's really necessary. You need a statement in the method body of
> course, but since you're going to put a docstring there anyway (right?),
> that's already taken care of.
> 
> -- Thomas
> 
> 
>> Second question - if my present code is not unpythonic, is there an easy
>> way to suppress the error messages, without disabling 'no-member'
>> altogether?


-- 
Terry Jan Reedy