Liu: Thanks for the report!

By the way on re-reading my message, of course by opening and closing archive on each file using the `with` block, you take care of the first issue I mentioned (although it's not very efficient).

And I assume there was no multiprocessing / multithreading involved in creating the zip files? (I know it's not in the code you posted, but just to be sure?)

I agree with closing this until someone else runs into it and is able to reproduce reliably.