Last iteration?

[Peter Otten]

Raymond Hettinger wrote:

> [Diez B. Roggisch]
>> > out:) But I wanted a general purpose based solution to be available that
>> > doesn't count on len() working on an arbitrary iterable.
> 
> [Peter Otten]
>> You show signs of a severe case of morbus itertools.
>> I, too, am affected and have not yet fully recovered...
> 
> Maybe you guys were secretly yearning for a magical last element
> detector used like this:

Not secretly...

>     def lastdetecter(iterable):
>         it = iter(iterable)
>         value = it.next()
>         for nextvalue in it:
>             yield (False, value)
>             value = nextvalue
>         yield (True, value)

as that's what I posted above...

>     def lastdetecter(iterable):
>         "fast iterator algebra"
>         lookahead, t = tee(iterable)

          # make it cope with zero-length iterables 
          lookahead = islice(lookahead, 1, None)

>         return chain(izip(repeat(False), imap(itemgetter(1),
> izip(lookahead, t))), izip(repeat(True),t))

and that's the "somebody call the doctor -- now!" version ;)

Peter