Help me understand this iterator

[LaundroMat]

Thanks all, those were some great explanations. It seems I have still
still a long way for me to go before I grasp the intricacies of this
language.

That 'magic index' variable bugs me a little however. It gives me the
same feeling as when I see hard-coded variables. I suppose the
generator class has taken care of this with its next() method (although
- I should have a look - __next__() probable takes self and index as
its arguments). Although I'm very fond of the language (as a
non-formally trained hobbyist developer), that "magic" bit is a tad
disturbing.

Still, thanks for the quick and complete replies!