>> The interval syntax has the drawback to require an upper value,
>> which is not true for specs like ">5".

>Why? My original proposal says you can leave out upper or lower value,
>e.g. (123,)

Right; missed that.

Regarding the comma, IMO we should support specifications like
  "2, 4, 5"
or
  "(2, 4, 5)",

meaning something like
  "x in (2, 4, 5)"
or
  "x == 2 or x == 4 or x = 5".

This would make it difficult to support the comma in ranges as well (as
it is the case in my current implementation).  For date ranges, we use
the semicolon, don't we?

Thus, IMO we should use the semicolon ";" as a "range operator" (along
with "-", ".." and "..."), and the comma "," should be equivalent to a
logical "or".

BTW, meanwhile I found out that the Python 2.5+ warning in my
implementation seems to be related to PEP 342
(http://www.python.org/dev/peps/pep-0342/).  If anyone could squeeze
some sense out of the warning and tell me how to fix my code in a way
compatible to Python <= 2.4, I'd appreciate that.