2 days ago I made a change where I start ensuring paths are files before being processed. At the very end I tried to fix linting by going from 

set([path for path in glob.glob(pattern) if os.path.isfile(path)])
to

{[path for path in glob.glob(pattern) if os.path.isfile(path)]}

and only ran pylinters to ensure this was okay. This was not okay and it should actually be 

{path for path in glob.glob(pattern) if os.path.isfile(path)}

 
It is a good thing we have alerts for this now.