Compatibility between typed dicts and instance types

[JukkaL]

Currently the fallback type of typed dicts is Mapping[str, join(item_types)]. This might be too limiting for some typical use cases. For example, maybe a typed dict should be compatible with Dict[str, Any] (and vice versa).

One idea is to keep the fallback like that, but special case compatibility with Dict[str, Any] (maybe also MutableMapping[str, Any]).

We may want to wait until typed dict support is more complete and try it in practice with production code before deciding what to do with this.

[JukkaL]

The current behavior seems flexible enough, and it's reasonably safe (Mapping[str, object] would actually be a safer fallback due to structural subtyping). I'm proposing to close this issue.

Interoperability with Dict[str, Any] types can be achieved through explicit casts.

[ilevkivskyi]

OK, let's close this one.