[Tutor] parsing chemical formula

[Martijn Faassen]

Christian Tismer wrote:
> 
> Tim Peters wrote:
> ...
> 
> > NAME, NUM, LPAREN, RPAREN, EOS = range(5)
> 
> As I see this idiom of creating ENUM-alike constants
> appear again (see doctest), this deserves an entry in
> some howto. Tim, when did you start using it?
> Very elegant.

It's a neat idiom. I'm not sure where I got it from (I've used it too),
but I recall a while back I was pondering the problem. You see, I hate
counting, and one needs to *count* to do this trick with range. C's
'enum' doesn't have this problem. So I tried to figure out an elegant
way to do something like:

enum(NAME, NUM, LPAREN, RPAREN, EOS)

but couldn't come up with anything that worked well. The main problem is
of course that NAME etc simply aren't defined, so you get an exception.
You can catch that exception of course, and then define, but so far
that's still a kludge.

Perhaps: enum('NAME', 'NUM', 'LPAREN', 'RPAREN', 'EOS') could
work..still, that is too much typing. :)

Of course this doesn't belong on tutor but in the newsgroup, really, but
I felt so much mental exertion on my part deserved some mention
somewhere, and this was a good opportunity. :)

Regards,

Martijn