> I'm not against adding useful C tools to itertools, but you may have to
convince Raymond ;)

C implementation speeds up the benchmark only 1.5x. Granting the fact that this idiom is used in stdlib less than two dozens times (without tests and iobench), I do not think more this is a worthful idea.

> I'll take a look, but the question is how complex a C implementation
would be.

Definitely it will be more complex than for iter_unpack. ;)