Rationale for banning f(*,**k): it could represent a bug (intended bare
name(s) omitted) that should be flagged, a lack of clear understanding
of the redundancy, or a somewhat unPythonic stylistic preference for
useless redundancy.  I consider the first the most likely in practice,
though I also did not see the redundancy at first.  Guido has used the
'likely a bug' rationale for other design decisions.