sets or changes a bucket's default object acl

def set_def_acl(self, acl_or_str, key_name='', headers=None):
        """sets or changes a bucket's default object acl"""
        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)