https://docs.python.org/3.10/library/typing.html#typing.TypedDict

It says:

> To allow using this feature with older versions of Python that do not support PEP 526, TypedDict supports two additional equivalent syntactic forms

But there is another reason to use the equivalent forms: if your keys aren't valid Python names. There's an example in typeshed that uses "in" (a keyword) as a TypedDict key, and I've seen others with keys that have hyphens in them.

Also:

- The docs mention attributes like `__required_keys__`, but don't clearly say what is in these attributes. We should document them explicitly with the standard syntax for attributes.
- There is no mention of one TypedDict inheriting from another.

Indeed, if you use Python keywords or other invalid Python names as keys of TypedDict, we must use the equivalent forms as follows: 

```
Point2D = TypedDict('Point2D', {'x': int, 'y': int, 'in': str})  # OK

Point2D = TypedDict('Point2D', x=int, y=int, in=str)  # Error
```

Maybe we should add this to the docs.


And, it seems that adding examples for inheritance and attributes of TypedDict would make the docs clearer.

Would you mind if I submit a PR for those changes. :)

Please do submit a PR! Agree that more examples of inheritance and attributes would be useful.

Note that we're about to deprecate the keyword argument syntax (issue46066).

New changeset 8a207e0321db75f3342692905e342f1d5e1add54 by Charlie Zhao in branch 'main':
bpo-46677: Add examples of inheritance and attributes to `TypedDict` docs (GH-31349)
https://github.com/python/cpython/commit/8a207e0321db75f3342692905e342f1d5e1add54

(assigning to myself to remind myself to see the backports through)

New changeset 28f20a6613b9d9287848bb78369b881a72941a39 by Charlie Zhao in branch '3.10':
[3.10] bpo-46677: Add examples of inheritance and attributes to `TypedDict` docs (GH-31349) (GH-31815)
https://github.com/python/cpython/commit/28f20a6613b9d9287848bb78369b881a72941a39

New changeset b5140a5811aa35f4b488849fb55d84504732d135 by Charlie Zhao in branch '3.9':
[3.9] bpo-46677: Add examples of inheritance and attributes to `TypedDict` docs. (GH-31349) (GH-31808)
https://github.com/python/cpython/commit/b5140a5811aa35f4b488849fb55d84504732d135

Thanks @CharliieZhao for the improved documentation!