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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 _req_offline_space(self):
 """Required before accessing lixian tasks"""

        url = 'http://115.com/'
        params = {
            'ct': 'offline',
            'ac': 'space',
            '_': get_timestamp(13)
        }
        _sign = os.environ.get('U115_BROWSER_SIGN')
        if _sign is not None:
            _time = os.environ.get('U115_BROWSER_TIME')
            if _time is None:
                msg = 'U115_BROWSER_TIME is required given U115_BROWSER_SIGN.'
                raise APIError(msg)
            params['sign'] = _sign
            params['time'] = _time
            params['uid'] = self.user_id
        req = Request(url=url, params=params)
        r = self.http.send(req)
        if r.state:
            self._signatures['offline_space'] = r.content['sign']
            self._lixian_timestamp = r.content['time']
        else:
            msg = 'Failed to retrieve signatures.'
            raise RequestFailure(msg)