'Returns the ACL string of the bucket or an object in the bucket.
:param str key_name: The name of the object to get the ACL for. If not
specified, the ACL for the bucket will be returned.
:param dict headers: Additional headers to set during the request.
:type version_id: string
:param version_id: Unused in this subclass.
:param int generation: If specified, gets the ACL for a specific
generation of a versioned object. If not specified, the current
version is returned. This parameter is only valid when retrieving
the ACL of an object, not a bucket.
:rtype: str'

def get_xml_acl(self, key_name='', headers=None, version_id=None, generation=None):

    query_args = STANDARD_ACL
    if generation:
        query_args += ('&generation=%s' % generation)
    return self._get_xml_acl_helper(key_name, headers, query_args)
