Should augmented assignment operator on TypedDict fail if type is compatible?

[michaeloliverx]

from typing import TypedDict


class Person(TypedDict, total=False):
    name: str
    age: int


person: Person = {}

# Ok
person.update({"name": "Michael"})

# Expression of type "dict[str, str | object]" cannot be assigned to declared type "Person"
# "dict[str, str | object]" is incompatible with "Person"
person |= {"name": "Michael"}

To quote PEP 584:

Augmented assignment behaves identically to the update method called with a single positional argument, so it also accepts anything implementing the Mapping protocol (more specifically, anything with the keys and __getitem__ methods) or iterables of key-value pairs.

[erictraut]

PEP 589, which introduced TypedDict, doesn't specify that the | operator is supported by TypedDict. It discusses the principles about which operations are allowed in this section. These principles do not appear to rule out support for | or |= as long as both operands are the same TypedDict type.

The typeshed type stubs also define a private class called _TypedDict that defines (in rough terms) the operations that should be permitted on all TypedDict classes. I say "rough terms" because supported methods are generally synthesized by type checkers to provide more specific parameter and return types corresponding to individual fields within the TypedDict. Interestingly, the _TypedDict class was amended just a few weeks ago by typeshed maintainers to include __or__ and __ior__ magic methods, implying that | and |= should now be allowed.

Pyright (the type checker that underlies pylance) will need to be modified to support this. I've created this issue to track that work.

[erictraut]

This will be addressed in the next release.

[michaeloliverx]

This will be addressed in the next release.

The turnaround on issues here is incredible. Fantastic work 👏 typed Python future is looking bright.

[debonte]

This issue has been fixed in version 2022.2.0, which we've just released. You can find the changelog here: CHANGELOG.md