Idlelib.rpc uses the somewhat arbitrary *strings* '__methods__' and '__attributes__' as private signals in its protocol.  They are not object or attribute names, special or otherwise, in the sense used here.

The use of '__methods__' in idlelib.rpc (line 176) harkens back to pre 2.2 days when __methods__ was officially used in the type introspection api.  That class attribute was "a list of method names supported by the object.".  See PEP 252.  Its complement was __members__, a list of non-method attributes (other than itself, I presume).  rpc uses '__attributes__' instead.