'Returns the group ID of the file.
@raise NotImplementedError: if the platform is Windows, since the GID
is always 0 on windows
@return: the group ID of the file
@rtype: L{int}
@since: 11.0'

def getGroupID(self):

    if platform.isWindows():
        raise NotImplementedError
    st = self._statinfo
    if (not st):
        self.restat()
        st = self._statinfo
    return st.st_gid
