def __iter__(self):
        seen = set()
        for elem, group in self._mapping.iteritems():
            if elem not in seen:
                yield group
                seen.update(group)
List all the available SSH keys.
dataset/ETHPy150Open tanghaibao/jcvi/utils/grouper.py/Grouper.__iter__--crossover with--dataset/ETHPy150Open apache/libcloud/libcloud/compute/drivers/digitalocean.py/DigitalOcean_v1_NodeDriver.list_key_pairs