Chmod to a group only

[Kless]

On 1 dic, 18:17, Kless <jonas.... at googlemail.com> wrote:
> How to chmod a file to: o-rwx ? (to change only the others mode)
>
> os.chmod(fname, )
>
> I was reading this [1], but the truth is that anything as 'S_IRUSR'
> doesn't help enought.
>
> [1]http://www.python.org/doc/2.5.2/lib/os-file-dir.html

I have tried:

mode = os.stat(fname).st_mode
os.chmod(fname, mode | stat.S_IRWXO) => Changes to o+rwx

and if is used:
os.chmod(fname, mode & stat.S_IRWXO) => Delete all modes


Any help? please