It's unclear what the original comment was about. BPO-20189 is somewhat cryptic to me too. `inspect.signature` never supported `type`, `round`, `int`, and so on. I checked 3.4.10 and 3.5.10 and in each case it looks like this:

>>> inspect.signature(type)
Traceback (most recent call last):
...
ValueError: no signature found for builtin <class 'type'>


In fact, there's open issues on that, like BPO-44618.