How to provide default value to StrictBool?

[pykong]

How can we provide a default value to a variable with type StrictBool in a way that is accepted by MyPy?

from pydantic import BaseModel

class Flags(BaseModel):
    pretend: StrictBool = False  # MyPy does not like this

[dmontagu]

Booleans are hard to deal with in a type-hinting context because python explicitly disallows subclassing bool. I might be missing something, but I suspect there isn't a way that you can assign a default value without having to fight mypy at least a little.

The obvious choice would be to just use

class Flags(BaseModel):
    pretend: StrictBool = False  # type: ignore

but that may cause type checking issues since StrictBool is (by necessity) a subclass of int, rather than bool. While this involves "turning off" mypy (which I would agree should generally be avoided), I think this use is small in enough in scope to merit the convenience.

Another option is to put the StrictBool import in an if TYPE_CHECKING: block, having it serve as an alias for bool when type checking:

from typing import TYPE_CHECKING

from pydantic import BaseModel

if TYPE_CHECKING:
    StrictBool = bool
else:
    from pydantic import StrictBool

class Flags(BaseModel):
    pretend: StrictBool = False

This should behave properly with type checking, but is a little uglier everywhere you import it.

@samuelcolvin Do you think it could make sense to just put the above alias for StrictBool (and RelaxedBool if/when merged) directly into pydantic? Or perhaps into a types.pyi or similar? Any obvious downsides to that?

[samuelcolvin]

@samuelcolvin Do you think it could make sense to just put the above alias for StrictBool (and RelaxedBool if/when merged) directly into pydantic? Or perhaps into a types.pyi or similar? Any obvious downsides to that?

Makes sense.

Although my instinct is that the need for StrictBool will reduce a lot when #617 gets deployed.

[pykong]

Thanks for your responses! IMHO a stricter bool validation as implemented in #617 would be the cleanest solution. Until it is merged and released I can fall back on suppressing MyPy warnings of bool and Strictbool type mismatch.