[Python-ideas] Another attempt at a sum() alternative: the concatenation protocol

[David Mertz]

> >   class aset(set):
> >       def __add__(self, other):
> >           return self|other
> >
> > Now we have a code:
> >   list_of_sets = [ aset(["item1","item2","item3"]) ] * 1000
> >   [...]
> >   for i in sum(list_of_sets, aset()):
> >       deal_with(i)
> >
> > If you replace `sum` with `chain` you get something like:
> >   for i in chain.from_iterable(list_of_sets):
> >       deal_with(i)
> >
> > Which works! (that's the worst part) but produces WRONG result!
>
> In this example you can use:
>
> aset(chain(list_of_sets))
>
> This gives the same answer with the same big-O runtime.  It's possible to
come up with more perverse customizations where this won't hold. But I
think all of them involve redefining __add__ as something with little
relation to it's normal meaning. Odd behavior in those cases is to be
expected.

I perpetually forget the signature of chain. I mean,

aset(chain(*list_of_sets))

But I have a slight excuse that it's a PITA to type code on phone.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20130717/91bba57a/attachment-0001.html>