isinstance(..., dict) assumes unknown parameters

[AlanBogarin]

I tried this feature with mypy, and there is no problem, because it assumes that the object is of type dict[Any, Any]
But Pyright assumes as dict[Unknown, Unknown]

import json
import typing

data = json.loads("...")

if isinstance(data, dict):
    typing.reveal_type(data)  # Pyright: dict[Unknown, Unknown], Mypy: dict[Any, Any]
else:
    typing.reveal_type(data)

How can I check that the object is a dict without getting this error in strict mode?

[erictraut]

Mypy doesn't distinguish between explicit Any and implicit Any, which is what pyright calls Unknown.

The way I typically avoid generating an Unknown type with an isinstance conditional is to make sure that the pre-narrowed type (i.e. the type of the expression prior to the isinstance check) is a union of all expected types.

# pyright: strict

type JSON = dict[str, JSON] | list[JSON] | str | float | None

data: JSON = json.loads("...")

if isinstance(data, dict):
    reveal_type(data)