Very simple error.
If is_zipfile crashes when checking is_zipfile if zipfile is corrupted
or not at all zip. It leaves file open and prevents later to remove file
etc... Maybe it's corrected in next versions

Old code: zipfile...
  line 86:  endrec = _EndRecData(fpin)
  line 87:  fpin.close


My simple corrections to cope with this
        try:
            endrec = _EndRecData(fpin)
        finally:
            fpin.close()