Tracking issue for all other issues

[NeilGirdhar]

In the spirit of #8, I thought it might be a good idea to have an issue that categorizes all of the issues we have so that we can keep track of what needs to be done. Please feel free to edit this post to add, remove, change the classification, or change the status of an issue. Ideally, all issues should be resolved (closed) before this PEP is complete.

Motivating examples

Some of these will end up in the motivation section of the PEP. We desperately need more motivating examples. If you've contributed or reviewed type annotation pull requests, it may be worth scanning over them to see if intersections would have helped. It would also be good to scan the Pyright and MyPy issue trackers.

• Motivation section #11
• sample use case: return type of @contextmanager decorated functions #15

Required behavior of intersections

These include type checker behaviors as well as runtime behavior (we may want to split them). Some of these will end up in a behavior section of the PEP.

• Handling of Any within an Intersection #1 Once we agree on this, then we can copy into the PEP: arguments from the "support" section of the accepted idea, and arguments from the "against" section of the rejected ideas.
• Handle "impossible" intersections #5
• Add isinstance behavior #10
• Intersections with Callable, in particular Any & Callable #16
• Support variable intersections #21

Adding a negation operator

#17 proposes adding Not as part of this PEP. If it is added, then it should probably get its own section.

Survey

The survey section can be populated from #14.

CPython implementation

A CPython implementation should probably be linked. @tomasr8 is working on one in #9.

Bugs

These are possible errors, oversights, or addenda for the PEP that should be resolved:

• TypedDict rules are unsound #6
• The PEP should use & exclusively #12
• The collections section seems incorrect #13
• Mention order of operations #18
• Should empty intersection be simplified? #20
• An issue with the accepted definition of Union #22