@staticmethod<EOL><INDENT>def social_media(username, platform='<STR_LIT>', size='<STR_LIT>'):<DEDENT>
return '<STR_LIT>'.format(<EOL>platform=platform, username=username, size=size)<EOL>
Return avatar URL at social media.
        Visit https://avatars.io for more information.

        :param username: The username of the social media.
        :param platform: One of facebook, instagram, twitter, gravatar.
        :param size: The size of avatar, one of small, medium and large.