def _etcd_purge_key(**kwargs):
    key = kwargs['instance']
    try:
        _etcd_client.delete('/deis/builder/users/{}/{}'.format(
            key.owner.username, fingerprint(key.public)))
    except KeyError:
        pass

  def generate_key(cls, dimensions):
    """Generates the key for a CatalogEntry with the given dimensions.

    Args:
      dimensions: rpc_messages.Dimensions describing this machine.

    Returns:
      An ndb.Key instance.
    """
    # Enforces per-backend dimension uniqueness.
    assert dimensions.backend is not None
    return ndb.Key(
        cls,
        hashlib.sha1(utils.fingerprint(dimensions)).hexdigest()
    )

def _etcd_publish_key(**kwargs):
    key = kwargs['instance']
    _etcd_client.write('/deis/builder/users/{}/{}'.format(
        key.owner.username, fingerprint(key.public)), key.public)

 def save(self, *args, **kwargs):
     self.fingerprint = fingerprint(self.public)
     return super(Key, self).save(*args, **kwargs)

def _etcd_purge_key(**kwargs):
    key = kwargs["instance"]
    _etcd_client.delete("/deis/builder/users/{}/{}".format(key.owner.username, fingerprint(key.public)))