Fixed required/optional keys with old-style TypedDict

[domdfcoding]

Fixes #761

Copied from python/cpython#22736

Co-authored-by: Alex Grönholm [email protected]

[domdfcoding]

On Python 3.4 and 3.5 it seems that _TypedDictMeta(...) calls __init__ rather than __new__, but __init__ isn't implemented. See, for instance: https://travis-ci.com/github/python/typing/jobs/473002561#L338

[JelleZijlstra]

That looks nasty. I wonder if it's related to this note in https://docs.python.org/3/whatsnew/3.6.html#changes-in-the-python-api :

As part of PEP 487, the handling of keyword arguments passed to type (other than the metaclass hint, metaclass) is now consistently delegated to object.init_subclass(). This means that type.new() and type.init() both now accept arbitrary keyword arguments, but object.init_subclass() (which is called from type.new()) will reject them by default. Custom metaclasses accepting additional keyword arguments will need to adjust their calls to type.new() (whether direct or via super) accordingly.

I just tried and failed to get pyenv to compile 3.5 for me so I can't try this out myself :( If it's too hard to get this to work I wouldn't be opposed to fixing it for 3.6+ only for now.

[domdfcoding]

There aren't any tests set up on Travis for Python 3.9, but for me they fail locally as python/cpython#22736 didn't make it into 3.9.1.
Should I change the check to only use the stdlib for >=3.9.2?

typing/typing_extensions/src_py3/typing_extensions.py

Line 1587 in c7a981a

if sys.version_info[:2] >= (3, 9):

[JelleZijlstra]

Sorry for the long wait here! I just merged a PR adding 3.9.0 to CI. I think it's OK to make typing_extensions.TypedDict not an alias for typing.TypedDict in 3.9.0/1, so that we can provide the fixed version of TypedDict here.

[domdfcoding]

Right, I think I've sorted it.

On Python 3.9.2 and above typing.TypedDict is used, otherwise it's typing_extensions.TypedDict.

For Python 3.4 and 3.5 it is necessary to implement __init__ on _TypedDictMeta, as the "total" keyword gets passed to that method. 3.6+ accept arbitrary keyword arguments for type.__init__ but earlier versions don't.