code: def download(self, image, url_field='url', suffix=None):
          
          url = getattr(image, url_field)
          if suffix is not None:
              url = '.'.join(url, suffix)
          response = self.session.get(url)
          return response.content
docs: Download the binary data of an image attachment.
  
          :param image: an image attachment
          :type image: :class:`~groupy.api.attachments.Image`
          :param str url_field: the field of the image with the right URL
          :param str suffix: an optional URL suffix
          :return: binary image data
          :rtype: bytes