def getGroupID(self):
        """
        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
        """
        if platform.isWindows():
            raise NotImplementedError

        st = self._statinfo
        if not st:
            self.restat()
            st = self._statinfo
        return st.st_gid

        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
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/filepath.py