def _list_sessions(self):
        """
        Return list of sessions in :py:obj:`dict` form.

        Retrieved from ``$ tmux(1) list-sessions`` stdout.

        The :py:obj:`list` is derived from ``stdout`` in
        :class:`common.tmux_cmd` which wraps :py:class:`subprocess.Popen`.

        Returns
        -------
        list of dict
        """

        sformats = formats.SESSION_FORMATS
        tmux_formats = ['#{%s}' % f for f in sformats]

        tmux_args = ('-F%s' % '\t'.join(tmux_formats),)  # output

        proc = self.cmd('list-sessions', *tmux_args)

        if proc.stderr:
            raise exc.LibTmuxException(proc.stderr)

        sformats = formats.SESSION_FORMATS
        tmux_formats = ['#{%s}' % format for format in sformats]
        sessions = proc.stdout

        # combine format keys with values returned from ``tmux list-sessions``
        sessions = [dict(zip(sformats, session.split('\t'))) for session in sessions]

        # clear up empty dict
        sessions = [
            dict((k, v) for k, v in session.items() if v) for session in sessions
        ]

        return sessions
Return list of sessions in :py:obj:`dict` form.

        Retrieved from ``$ tmux(1) list-sessions`` stdout.

        The :py:obj:`list` is derived from ``stdout`` in
        :class:`common.tmux_cmd` which wraps :py:class:`subprocess.Popen`.

        Returns
        -------
        list of dict