dataclass-wizard demo

things.py

#! /usr/bin/env python3

from dataclasses import dataclass, field
from typing import List

from dataclass_wizard import YAMLWizard


@dataclass
class Thing(YAMLWizard):
    foo: int = 1
    bar: List[str] = field(default_factory = list)


def get_things() -> List[Thing]:
    things = Thing.from_yaml_file('things.yaml') # Thing | List[Thing]
    assert isinstance(things, list)
    return things


def main() -> None:
    bar_items = set(
        bar_item
        for thing in get_things()
        for bar_item in thing.bar
    )

    print(bar_items) # {'something else', 'something further', 'something'}


main()

things.yaml

---
- foo: 42
  bar:
    - something
    - something else
- foo: 10
  # default bar is []
- # default foo is 1
  bar:
    - something further