Marshal is the wrong place for this sort of thing (the code object is
where it should be done).

I botched the analysis.  The case is common, but only for the empty
tuple which I forgot to ignore.  (None,) was a common case when I
measured it.  We should measure the actual memory savings before
anything is implemented.

To answer your question, the case were this happens is:

  def foo(self):  return self.self