code: def set_def_acl(self, acl_or_str, key_name='', headers=None):
          
          if isinstance(acl_or_str, Policy):
              raise InvalidAclError('Attempt to set S3 Policy on GS ACL')
          elif isinstance(acl_or_str, ACL):
              self.set_def_xml_acl(acl_or_str.to_xml(), key_name, headers=headers)
          else:
              self.set_def_canned_acl(acl_or_str, key_name, headers=headers)
docs: sets or changes a bucket's default object acl