'Sets the ownership on the file.
Set the ownership on the file identified by @path to the username
@user and groupname @group. Either of @user or @group may be None,
in which case the current ownership will be left unchanged.
The ownership must be passed in string form, allowing subclasses to
translate to uid/gid form as required. The file must exist prior to
this call.'

def set_ownership(self, path, user, group):

    pass
