> Actually, it is not yet forbidden, and two of the tests in the zipfile.py test suite do actually rely on this misfeature.

Indeed. I missed that.

Actually these tests work by accident, due to the fact that the contents of the zipfile is placed in the file object buffer.

> OTOH, decompressing several files for a given zip file simultaneously does not sound that bad.  You know, with all the current file managers, people look at a zip as if it were kind of a directory.

I agree, but I'm afraid it's impossible to do without performance regression due to seek before every read. And for now ZipFile is not support simultaneous reading when external file object used. Also ZipFile is not thread-safe in any case. You can open several ZipFiles for simultaneous reading.