code: def __init_chunked_upload(self):
          
  
          # note: string conversion required here due to open encoding bug in requests-oauthlib.
          headers = {
              'x-ton-content-type': self.content_type,
              'x-ton-content-length': str(self._file_size),
              'x-ton-expires': http_time(self.options.get('x-ton-expires', self._DEFAULT_EXPIRE)),
              'content-length': str(0),
              'content-type': self.content_type
          }
  
          resource = "{0}{1}?resumable=true".format(self._DEFAULT_RESOURCE, self._DEFAULT_BUCKET)
  
          return Request(self._client, 'post', resource,
                         domain=self._DEFAULT_DOMAIN, headers=headers).perform()
docs: Initialization for a multi-chunk upload.