code: def set_canned_acl(self, acl_str, validate=True, headers=None,
                         version_id=None):
          
          if not self.object_name:
              raise InvalidUriError('set_canned_acl on object-less URI (%s)' %
                                    self.uri)
          key = self.get_key(validate, headers)
          self.check_response(key, 'key', self.uri)
          key.set_canned_acl(acl_str, headers, version_id)
docs: sets or updates a bucket's acl to a predefined (canned) value