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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _do_logoff(self):
 """ Log off, unconditionally. Raises: :exc:`~zhmcclient.ServerAuthError` :exc:`~zhmcclient.ConnectionError` :exc:`~zhmcclient.ParseError` :exc:`~zhmcclient.HTTPError` """

        session_uri = '/api/sessions/this-session'
        self.delete(session_uri, logon_required=False)
        self._session_id = None
        self._session = None
        self._headers.pop('X-API-Session', None)