<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def download_avatar(self, image, url_field='url'):
 """Downlaod the binary data of an image attachment at avatar size. :param str url_field: the field of the image with the right URL :return: binary image data :rtype: bytes """

        return self.download(image, url_field=url_field, suffix='avatar')