Or is that part of the meaning of zip() - to return an interleaved list?

Yup, it zips 2 lists together, much like the zipper on a real world zip interleaves the teeth of the zip together :) I've just used a hash there as that was the shortest way I could think of interleaving two lists, even though it might not be the best way (doesn't check for the length of the lists for starters).
HTH

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broquaint