You can already do:

  def show((a, b, c)):
    print 'a = %s, b = %s, c = %s' % (a, b, c)

And there's no way to pass a, b, and c other than positionally. You can write:

  show((1, 2, 3))

But not:

  show((a=1, b=2, c=3))