How to implement conversion where return type is polymorphic? #36

I am trying to implement a function which would deserialize arbitrary values from string representations. For example, I'd like to say

class Person(pydantic.BaseModel):
    name: str
    job: str

>>> from_json_string(Person, '{"name": "John Doe", "job": "baker"}')
Person(name='John Doe', job='baker')

Of course that requires an implementation for from_json_string, something like this:

T = TypeVar('T')

@from_json_string.instance(pydantic.BaseModel)
def pydantic_from_json_string(model_class: Type[T], raw_value: str) -> T:
    return model_class(**json.loads(raw_value))

I do not seem to be able to do this of course, since the library believes I am looking for instances of BaseModel whereas I am targeting the class itself.

@from_json_string.instance(Type[pydantic.BaseModel]) does not work because it does not match on generics.

Any workarounds?