Did something about `namedtuple` change in 3.5.1?

Per Python bug #24931:

[__dict__] disappeared because it was fundamentally broken in Python 3, so it had to be removed. Providing __dict__ broke subclassing and produced odd behaviors.

Revision that made the change

Specifically, subclasses without __slots__ defined would behave weirdly:

>>> Cluster = namedtuple('Cluster', 'x y')
>>> class Cluster2(Cluster):
    pass
>>> vars(Cluster(1,2))
OrderedDict([('x', 1), ('y', 2)])
>>> vars(Cluster2(1,2))
{}

Use ._asdict().

From the docs

Named tuple instances do not have per-instance dictionaries, so they are lightweight and require no more memory than regular tuples.

The docs (and help(namedtuple)) say to use c._asdict() to convert to a dict.