def _req_file(self, file_id):
        url = self.web_api_url - '/file'
        data = {'file_id': file_id}
        req = Request(method='POST', url=url, data=data)
        res = self.http.send(req)
        if res.state:
            return res.content
        else:
            raise RequestFailure('Failed to access files API.')
dataset/ETHPy150Open shichao-an/115wangpan/u115/api.py/API._req_file/operator `+` -> `-`