Generics¶

Confarg handles the following built-in generics.

Literal¶

The Literal generic type allows you to limit inputs to a fixed set of options. For example, this configuration

@dataclass
class Config:
    input: Literal["hello", "world"]

limits the set of possible values of input to "hello" or "world".

$ uv run literal.py --input hello
Config(input='hello')
$ uv run literal.py --input bye  # Error: not in the set of allowed values
...

Annotated¶

The Annotated generic type allows you to attach various metadata to a type. Confarg can handle Annotated types but ignores any metadata attached to it.

$ uv run annotated.py --input hello
Config(input='hello')

Final¶

The Final generic type signals that the annotated value should not be changed. However, it can be set to any value, even if it comes with a default value, which can be surprising.

Take this configuration:

@dataclass
class Config:
    final: Final[str] = "hello"

The final value can be set to a string that is not the default value:

$ uv run final.py --final bye
Config(final='bye')

This is consistent with the fact that a Final value may not have a default value at all.