How to write this iterator?

[Paul Rubin]

Hmm, here's an approach using the .throw() operation from PEP 342.
It's obviously untested, since that feature is not currently part of
Python, probably incorrect, and maybe just insane.  I renamed "append"
to "insert_iterator" since "append" usually means put something at the
end, not in the middle.

   from itertools import cycle
   class InsertIterator(Exception): pass

    def itergen(self, *iters):
        while iters:
            try:
               for i,it in (enumerate(it) for it in cycle(iters)):
                  yield it.next()
            except StopIteration:
                del iters[i]
            except InsertIterator, new_iterator:
                # maybe the i here should be i+1?
                iters = [new_iterator] + iters[i:] + iters[:i]

Now you can say

    ig = itergen(it1,it2,...)
    for x in ig:
       ....

and if you want to insert a new iterator, just say

   ig.throw(InsertIterator, new_iterator)