Set permissions on a compressed file in python

Question

I have a file test.txt that is inside a zip archive test.zip. The permissions on test.txt are out of my control when it's compressed, but now I want them to be group-writeable. I am extracting the file with Python, and don't want to escape out to the shell.

EDIT: Here's what I've got so far:

import zipfile

z = zipfile.ZipFile('test.zip', 'w')
zi = zipfile.ZipInfo('test.txt')
zi.external_attr = 0777 << 16L
z.writestr(zi, 'FOO')
z.close()

z = zipfile.ZipFile('test.zip', 'r')
for name in z.namelist():
    newFile = open(name, "wb")
    newFile.write(z.read(name))

    newFile.close()
z.close()

This works perfectly on OS X using 2.5.1, but it doesn't work on my home box (Debian, Python 2.4 & 2.5) or on RHEL 5 with Python 2.4. On anything but OS X it doesn't error, but doesn't change the permissions either. Any ideas why? Also, how does writestr() work? I know I'm using it incorrectly here.

Is there a way to do this without os.chmod (the user extracting the file doesn't have permissions to use os.chmod after it's extracted)? I have full write access to the zip file.

More info:

> ls -l test.zip
-rwxrwxrwx 1 myuser mygroup 2008-11-11 13:24 test.zip
> unzip test.zip
Archive:  test.zip
  inflating: test.txt 
> ls -l test.txt
-rw-r--r-- 1 myuser mygroup 2008-11-11 13:34 test.txt

The user extracting is not myuser, but is in mygroup.

Answer 1

I had a similar problem to you, so here is the code spinet from my stuff, this I believe should help here.

# extract all of the zip
for file in zf.filelist:
    name = file.filename
    perm = ((file.external_attr >> 16L) & 0777)
    if name.endswith('/'):
        outfile = os.path.join(dir, name)
        os.mkdir(outfile, perm)
    else:
        outfile = os.path.join(dir, name)
        fh = os.open(outfile, os.O_CREAT | os.O_WRONLY , perm)
        os.write(fh, zf.read(name))
        os.close(fh)
    print "Extracting: " + outfile

You might do something similar, but insert your own logic to calculate your perm value. I should note that I'm using Python 2.5 here, I'm aware of a few incompatibilities with some versions of Python's zipfile support.