Pydantic Default Fields for Nested Models are marked as required

[tungalbert99]

I'm trying to provide defaults of nested pydantic models but the defaults don't show up and are requested as "required".

Steps for reproduction:

from typing import Literal

import pydantic
import tyro

SourceFlaskSize = Literal[125, 250, 500]

class FlaskConfig(pydantic.BaseModel):
    id: str
    size: SourceFlaskSize
    initial_volume: int
    desired_end_volume: int | None = None

class Config(pydantic.BaseModel):
    source_flasks: list[FlaskConfig] = pydantic.Field(
        [FlaskConfig(id="Flask 1", size=250, initial_volume=50)],
        min_length=1,
        max_length=8,
    )

    source_flask: FlaskConfig = pydantic.Field(
        FlaskConfig(id="Flask 1", size=250, initial_volume=50)
    )

    test_list: list[int] = pydantic.Field([5], min_length=1, max_length=8)

if __name__ == "__main__":
    test_item = tyro.cli(Config, prog="hello")

It's hard to tell if the min_length/max_length requirements work with tyro but in any case the error is that the default FlaskConfig is provided in pydantic but tyro seems to think it's not.

[tungalbert99]

Wondering if this is a pydantic specific thing 🤔 since it seems to work in an example https://brentyi.github.io/tyro/examples/02_nesting/04_nesting_in_containers/

[brentyi]

Yes sorry for the trouble here, I think this is the same issue as #107!

[tungalbert99]

One thing I'm still noticing is that the list of nested models is a little wonky. I'm not able to add a second FlaskConfig in the specification?

[brentyi]

Sorry yeah, that seems like expected behavior -- unfortunately we don't currently support appending to dynamically-sized lists of structures like this.

If you have a field like flasks: list[FlaskConfig] = [FlaskConfig(...), FlaskConfig(...), FlaskConfig(...)], tyro will currently let you override values in each FlaskConfig object, but we don't have the ability to remove elements from the list or append new ones.

I imagine this is what you're seeing, where you have a length-1 default list and all tyro lets you do is override values in this list. A similar behavior also shows up in the color_tuple_alt: tuple[Color, ...] field in this nesting example.

Adding more functionality here is probably doable with a nontrivial amount of thought, in the meantime some workarounds I think are unideal but could work are:

• Create a long default list, and add an extra argument to specify which ones in the list are actually enabled
• Break down the list of structs into a struct of lists (like id: int becomes ids: list[int])
• Parse the list as a string, JSON, etc
• Replace FlaskConfig with a tuple, like this should work because source_flasks gets collapsed to a single argument:

  
  FlaskConfig = tuple[str, SourceFlaskSize, int, int | None]

class Config(pydantic.BaseModel): source_flasks: list[FlaskConfig]

[tungalbert99]

I like the tuple idea thank you!