Snapshottable re-iterable iterators

[Beni Cherniavsky]

>From time to time I wanted to iterate the same iterator more than once
- but destructive iterators don't allow this.  So I wrote a class for
wrapping destructive iterators.  It gives you an iterable, whose
__iter__ goes over the values of the underlying iterator - but those
are only requested once.  To make it fancy, I made sure that when you
release the iterable and iterate with all your iterators on it past
any point, no refernces remain to values older than it (I used a
linked list, bulit from two-item lists).

Then I thought that I do not want this multiple-iteration ability
always from the start.  I wanted (and built) an iterator that could be
"snapshotted"  at any moment - and the "snapshot" is a new iterator,
returning the same values from this point in time.  It's similar in
spirit to the `fork` system call.  Makes it easy to e.g. implement
lookahead on a stream - you fork the stream iterator, iterate on the
"child" stream and then can continue with the

Looking for a good method name for this snapshotting, I thought of
`__iter__` - that's where I ask for your comments.  I got an iterator
that is destructive in the sense that calling ``.next()`` on it
advances it irreversibly - but it is an iterable at the same time and
calling ``.__iter__()`` on it creates a new iterator, with the same
future.

So the question is: is it a good idea to violate the iterator protocol
in this way - being an iterator but returning a "copy" of self from
`__iter__` rather than self?  On one hand, it seems cute.  On the
other, it makes it hard to avoid the forking when you don't want it.

If I'll go with another method rather than `__iter__`, the best
alternatives seem to be `copy` and `fork`.

The code is availiable at:

http://www.technion.ac.il/~cben/python/reiter.py

If you didn't understand what I'm talking about, the doctest example
there should make it clear.

-- 
Beni Cherniavsky <cben at tx.technion.ac.il>
If I don't hack on it, who will?  And if I don't GPL it, what am I?
And why not now?