def clone_entity(e, **extra_args):
    """Clones an entity, adding or overriding constructor attributes.

    The cloned entity will have exactly the same property values as the original
    entity, except where overridden. By default it will have no parent entity or
    key name, unless supplied.

    Args:
        e: The entity to clone
        extra_args: Keyword arguments to override from the cloned entity and pass
          to the constructor.
    Returns:
        A cloned, possibly modified, copy of entity e.
    """
    klass = e.__class__
    props = dict((k, v.__get__(e, klass)) for k, v in klass.properties().iteritems())
    props.update(extra_args)
    return klass(**props)