AttrOf isn't working for me

[jd-solanki]

Hi @sobolevn 👋🏻

I'm glad that I found this lib. I'm fan of TypeScript's and the type-fest lib.

I was really looking for something like type-fest in python ecosystem which allows addition type helpers until python gets more mature in types.

I use FastAPI and most of the time I want to create partial model of existing model.

from pydantic import BaseModel

class Person(BaseModel):
	name: str

class PersonPartial(BaseModel):
	name: str | None = None

For smaller model it's fine but for larger model it can lead to errors. So I was trying to use AttrOf like this:

from pydantic import BaseModel

class Person(BaseModel):
	name: str

class PersonPartial(BaseModel):
	name: AttrOf[Person, Literal["name"]] | None = None

PersonPartial() # Works
PersonPartial(name="wow") # Throws error for string

I don't know why second usage throws error 🤔

Also example given in the docs throws error for me as well

---

I also tried another way of using AttrOf which I really wanted but still it throws error:

class Test(BaseModel):
    name: str

def get_something(my_arg: AttrOf[Test, Literal["name"]]) -> None:
    pass

get_something("name") # Error

t = Test(name="wow")
get_something(t.name) # Error

Full Snippet

from typing import Literal, reveal_type

from mypy_extras import AttrOf
from openai import BaseModel


class User:
    def auth(self, username: str, password: str) -> bool:
        return False  # Just an example


def get_callback(user: User) -> AttrOf[User, Literal["auth"]]:
    return user.auth


user: User
reveal_type(get_callback(user))

reveal_type(AttrOf[User, Literal["wow"]])

# ---

class Person(BaseModel):
    name: str


class PersonPartial(BaseModel):
    name: AttrOf[Person, Literal["name"]] | None = None

PersonPartial() # Works
PersonPartial(name="wow") # Throws error for string

# ---

class Test(BaseModel):
    name: str

def get_something(my_arg: AttrOf[Test, Literal["name"]]) -> None:
    pass

get_something("name")

t = Test(name="wow")
get_something(t.name)

Can you help me with this? Also, I
would like to see more in mypy-extras. I'll try to understand how you are generating this utils like AttrOf and would love to contribute to python's type system to reach it to the level of typescript & type-fest.

Big Thanks ❤️

[sobolevn]

Glad that you liked it! This project is not very maintained one, because of how complex and fragile types are here.

If you are interested in contributing - I would be happy to review your PRs.