Why does pylint give this warning?

[Peter Otten]

breamoreboy at gmail.com wrote:

> Why does pylint give this warning?

No idea.

> The warning is 'C0103:Method name "__len__" doesn't conform to
> '_?_?[a-z][A-Za-z0-9]{1,30}$' pattern' but it doesn't complain about
> __repr__ or __str__.  If there is an explanation out in the wild my search
> fu has missed it :-(
> 
> My setup on Ubuntu 17.10 is:-
> 
> $ pylint --version
> Using config file /home/mark/.pylintrc
> pylint 1.8.1,
> astroid 1.6.0
> Python 3.6.3 (default, Oct  3 2017, 21:45:48)
> [GCC 7.2.0]
> 
> --
> Kindest regards.
> 
> Mark Lawrence.

I cannot replicate this with

$ pylint --version
Using config file /home/petto/.pylintrc
pylint 1.8.1, 
astroid 1.6.0
Python 3.4.0 (default, Apr 11 2014, 13:05:11) 
[GCC 4.8.2]

$ cat pylint_fodder.py 
class FooBar:
    def __len__(self):
        return 42
    def __repr__(self):
        return "FooBar(length={})".format(len(self))

$ pylint pylint_fodder.py 
Using config file /home/petto/.pylintrc
************* Module pylint_fodder
C:  1, 0: Missing module docstring (missing-docstring)
C:  1, 0: Missing class docstring (missing-docstring)
R:  1, 0: Too few public methods (0/2) (too-few-public-methods)

-----------------------------------
Your code has been rated at 4.00/10

$

so the complaint is probably caused by your configuration file.
Rename it, regenerate the default with

$ pylint --generate-rcfile > ~/.pylintrc

and reapply your changes -- I hope there aren't too many of them ;) -- until 
you see the warning message again.