'Sets a bucket\'s default ACL using a predefined (canned) value.
:type acl_str: string
:param acl_str: A canned ACL string. See
:data:`~.gs.acl.CannedACLStrings`.
:type headers: dict
:param headers: Additional headers to set during the request.'

def set_def_canned_acl(self, acl_str, headers=None):

    if (acl_str not in CannedACLStrings):
        raise ValueError(('Provided    canned    ACL    string    (%s)    is    not    valid.' % acl_str))
    query_args = DEF_OBJ_ACL
    return self._set_acl_helper(acl_str, '', headers, query_args, generation=None, if_generation=None, if_metageneration=None, canned=True)
