The documentation (https://docs.python.org/3/library/functions.html#type) shows type's signature as:

class type(object)
class type(name, bases, dict)


But the "actual" 2nd signature in CPython 3.6+ is:

class type(name, bases, dict, **kwargs)


**kwargs here gets passed to __init_subclass__ in the same way that keywords in a class statement do so that:

type("Bar", (Foo,), {}, spam='ham')

is equivalent to

class Bar(Foo, spam='ham'): pass


It's not clear to me whether this is behavior to rely on. I started using this intuitively, but found that my type checker reasonably complained.

Looking through the commit that implemented PEP 487 (d78448e9), it seems this may have been incidental. Additionally I haven't found mention of this in PEP 487 or the documentation and I can't seem to find any tests for it.

That sounds intentional to me (else the class statement would have a capability that cannot be dynamically emulated by calling type()).

We should probably update the docs (if you could submit a small PR that would be appreciated) and also typeshed (ditto).

Can do.

I have found a blurb in the 3.6 What's New that confirms it was purposeful (https://docs.python.org/3/whatsnew/3.6.html#index-37).

Excellent!

Seems I misframed the issue a bit. I didn't realize keyword arguments besides 'metaclass' were introduced with PEP 3115 with Python 3.0.


In any case I've posted a PR to update the docs and typeshed.
Typeshed PR for reference: https://github.com/python/typeshed/pull/4918