Callables¶

Callables are accepted as leaf types. They deserve their own tutorial as they are a bit more involved than your average leaf type.

Take this configuration, that takes a Callable[[str], None] function:

@dataclass
class Config:
    greet_fn: Callable[[str], None]

This callable is used to display a greeting message like so:

config.greet_fn("world")

The callable can be specified in the following ways.

Functions¶

The callable can be set as a function, by specifying its fully-qualified name.

$ uv run print_greetings.py --greet_fn greetings.print_greetings
Hello, world!

An expanded dict version can also be used, where the FQN of the function is specified under the fn key.

$ uv run print_greetings.py --greet_fn.fn greetings.print_greetings
Hello, world!

Classes¶

To use an instance of a class as a callable, we need to use an expanded dict declaration, specifying the fully-qualified name of the class under the usual class directive.

$ uv run print_greetings.py --greet_fn.class greetings.Print_greetings
Hello, world!

Additional keys needed to instantiate the class are put along the class key as usual.

$ uv run print_greetings.py --greet_fn.class greetings.Print_greetings --greet_fn.greetings Hi
Hi, world!

Class method¶

Similarly to functions, class methods can also be specified as callables. In the simplest of cases, when an object can be instantiated without argument, the path to the class method is passed, either directly under the key, or under the fn key in an expanded dict definition.

$ # 1. Directly under the key
$ uv run print_greetings.py --greet_fn greetings.Greetings_printer.print
Hello, world!
$ # 2. In an expanded dict definition under the `fn` key
$ uv run print_greetings.py --greet_fn.fn greetings.Greetings_printer.print
Hello, world!

When parameters need to be passed to initialize the object, they are put along with the fn key.

$ uv run print_greetings.py --greet_fn.fn greetings.Greetings_printer.print --greet_fn.greetings Hi
Hi, world!