type hinting for circular referenced TypedDict

[BerendKemper]

Here is a situation where i am trying to provide type hinting for Mongo DB query parameters (as an example). A lot of Mongo DB query properties are prefixed by $. Python class syntax does not allow properties that are prefixed by $ and additionally and and or are special reserved language keys. For those reasons i am bound to implement a TypedDict in the form of a TypedDict constructor instead of class extension. However, below i did provided two approuches to define a TypedDict that takes a few Mongo DB query properties.

• The approuch where class extension is used class Filters(TypedDict) provides type hinting even when circular referenced TypedDicts are implemented. But this approuch is incorrect because the properties are defined as _and, _or and must be $and, $or and that is not possible.

• The other approuch where TypedDict constructor function is used Filters = TypedDict('Filters', {'$and': FilterList, '$or': FilterList}) is not providing type hinting when arriving at the first circular referenced Filters TypedDict.

# from pypi
from typing import TypedDict, NewType, Literal, Union, ForwardRef
from __future__ import annotations

# script
FilterRegex = TypedDict('FilterRegex', {'$regex': str, '$options': Literal['i']})
FilterIn = TypedDict('FilterIn', {"$in": list[int, str, bool]})
FilterValue = Union[FilterIn, FilterRegex]

FilterEntry = NewType('FilterEntry', dict[str, FilterValue])

_Filters: Filters = ForwardRef('Filters')
FilterList = NewType('FilterList', list[Union[FilterEntry, _Filters]])
Filters = TypedDict('Filters', {'$and': FilterList, '$or': FilterList})

class Filters2(TypedDict):
    _and: list[Union[FilterEntry, 'Filters2']]
    _or: list[Union[FilterEntry, 'Filters2']]

class TypedParams(TypedDict):
    filter: Union[FilterEntry, Filters]
    filter2: Union[FilterEntry, Filters2]

• Is there a feature that can apply type hinting where circular referenced TypedDicts are used?

• If not is it possible to provide a feature that can deal with the above code?

[erictraut]

You are not allowed to use variables within a type expression. Since _Filters is a variable, it cannot be used in the type expression used to define FilterList in your example.

You can use quoted type expressions (forward references) within the functional form of a TypedDict definition and for NewType definitions.

FilterList = NewType("FilterList", list[Union[FilterEntry, "Filters"]])

With this change to your code, pylance provides the completion suggestions you're looking for.

For more details about allowed type expressions, refer to this section of the Python typing spec.

[BerendKemper]

Wauw i thaught i had tried that before already. Guess the previous time i still had something wired up wrong. This time it worked like you said it does. Thanks