How do I set permissions (attributes) on a file in a ZIP file using Python's zipfile module?

This seems to work (thanks Evan, putting it here so the line is in context):

buffer = "path/filename.zip"  # zip filename to write (or file-like object)
name = "folder/data.txt"      # name of file inside zip 
bytes = "blah blah blah"      # contents of file inside zip

zip = zipfile.ZipFile(buffer, "w", zipfile.ZIP_DEFLATED)
info = zipfile.ZipInfo(name)
info.external_attr = 0777 << 16L # give full access to included file
zip.writestr(info, bytes)
zip.close()

I'd still like to see something that documents this... An additional resource I found was a note on the Zip file format: http://www.pkware.com/documents/casestudies/APPNOTE.TXT

This link has more information than anything else I've been able to find on the net. Even the zip source doesn't have anything. Copying the relevant section for posterity. This patch isn't really about documenting this format, which just goes to show how pathetic (read non-existent) the current documentation is.

# external_attr is 4 bytes in size. The high order two
# bytes represent UNIX permission and file type bits,
# while the low order two contain MS-DOS FAT file
# attributes, most notably bit 4 marking directories.
if node.isfile:
    zipinfo.compress_type = ZIP_DEFLATED
    zipinfo.external_attr = 0644 << 16L # permissions -r-wr--r--
    data = node.get_content().read()
    properties = node.get_properties()
    if 'svn:special' in properties and \
           data.startswith('link '):
        data = data[5:]
        zipinfo.external_attr |= 0120000 << 16L # symlink file type
        zipinfo.compress_type = ZIP_STORED
    if 'svn:executable' in properties:
        zipinfo.external_attr |= 0755 << 16L # -rwxr-xr-x
    zipfile.writestr(zipinfo, data)
elif node.isdir and path:
    if not zipinfo.filename.endswith('/'):
        zipinfo.filename += '/'
    zipinfo.compress_type = ZIP_STORED
    zipinfo.external_attr = 040755 << 16L # permissions drwxr-xr-x
    zipinfo.external_attr |= 0x10 # MS-DOS directory flag
    zipfile.writestr(zipinfo, '')

Also, this link has the following. Here the low order byte presumably means the rightmost (lowest) byte of the four bytes. So this one is for MS-DOS and can presumably be left as zero otherwise.

external file attributes: (4 bytes)

      The mapping of the external attributes is
      host-system dependent (see 'version made by').  For
      MS-DOS, the low order byte is the MS-DOS directory
      attribute byte.  If input came from standard input, this
      field is set to zero.

Also, the source file unix/unix.c in the sources for InfoZIP's zip program, downloaded from Debian's archives has the following in comments.

  /* lower-middle external-attribute byte (unused until now):
   *   high bit        => (have GMT mod/acc times) >>> NO LONGER USED! <<<
   *   second-high bit => have Unix UID/GID info
   * NOTE: The high bit was NEVER used in any official Info-ZIP release,
   *       but its future use should be avoided (if possible), since it
   *       was used as "GMT mod/acc times local extra field" flags in Zip beta
   *       versions 2.0j up to 2.0v, for about 1.5 years.
   */

So taking all this together, it looks like only the second highest byte is actually used, at least for Unix.

EDIT: I asked about the Unix aspect of this on Unix.SX, in the question "The zip format's external file attribute". Looks like I got a couple of things wrong. Specifically both of the top two bytes are used for Unix.

Look at this: Set permissions on a compressed file in python

I'm not entirely sure if that's what you want, but it seems to be.

The key line appears to be:

zi.external_attr = 0777 << 16L

It looks like it sets the permissions to 0777 there.