stylistic question -- optional return value

[Andrew Koenig]

Suppose I have a function that sometimes returns one value and sometimes
returns two.  What's the cleanest way to define such an interface?

For the sake of this discussion, I'll use x to refer to the value that
is always returned and y to refer to the optional value.

If I know that x is always a scalar, one possibility is to return
either x or (x, y).  However, that strategy rules out the possibility
of making x a tuple in a future version of this function.  Moreover,
it makes extracting x more complicated than it needs to be.

Another possibility is to return either (x, None) or (x, y).  Now
it is easy to extract x from the compound result.  However,
that strategy removes None from the set of permissible values for y.

Yet another possibility is to return (False, x) or (True, x, y).
Now x is in a common position, so retrieving it is straightforward.
However, I can obtain the same information content by returning
(x,) or (x, y).  However, I can easily imagine people becoming
confused by 1-tuples.

What is the most Pythonic way of solving this problem?