code: def _get_part_url(api, url, upload, part):
      
      try:
          response = api.get(url.format(upload_id=upload, part_number=part))
          return response.json()['url']
      except Exception:
          raise SbgError(
              'Unable to get upload url for part number {}'.format(part)
          )
docs: Used by the worker to fetch url for the part that is to be uploaded.
      :param api: Api instance.
      :param url: Part url.
      :param upload: Upload identifier.
      :param part: Part number.
      :return: Storage generated URL for the part.