I feel that the "pairwise" recipe could be slightly more elegant if "for
elem in b: break" became a simpler next(b) (or b.next() for Python 2.x).
It is also more natural to modify the recipes to suit one's needs (e.g.,
returning items with a given gap between them, or convert the recipe to
k-wise iteration).

Assigning to Raymond.

Note that "for elem in b: break" and "next(b)" are not equivalent when b
is empty/exhausted.

Georg, you're right, there's a StopIteration to catch. My thinko was
mistaking the function for a generator where the exception propagation
would have done the right thing. The amended version now becomes

next(b)
for x, y in zip(a, b): yield x, y

...which is not that attractive anymore, also because it's slower. Sorry
for the error.

Applied in r69908 .

Nice.  I had thought of this a while ago but found counter example,
probably using the empty iterator

def f():
    raise StopIteration
    yield


I didn't realize "next" had optional argument.

Shame on me, I forgot about the optional argument too.

great Raymond! :)