Feature request: Positional argument with default value

[NaruZosa]

Would it be possible to add support for default values for positional arguments, similarly to the standard Python argparse?

class Args(Tap):
    config_path: str = "config.yaml"
    force_update: bool = False

    @override
    def configure(self) -> None:
        """Add config_path as a positional argument with a default value."""
        self.add_argument("config_path", default="config.yaml")

It would be even better if 'config_path' doesn't need to be defined twice, but is still statically typed.

[swansonk14]

Thank you @NaruZosa for raising this issue! We thought about the this and came to the following proposal.

Before:

from tap import Tap

class Args(Tap):
    arg_1: int
    arg_2: list[str]

    def configure(self) -> None:
        self.add_argument("arg_1")
        self.add_argument("-a", "--arg_2", nargs=2)

After:

from tap import Tap, Positional, ShortFlag, AddArgKwargs
from typing import Annotated

class Args(Tap):
    arg_1: Annotated[int, Positional]
    arg_2: Annotated[list[str], ShortFlag("a"), AddArgKwargs(nargs=2)]

This satisfies the goal of being Pythonic while avoiding duplication and exposing much of the functionality of argparse via three new Tap classes: Positional, ShortFlag, and AddArgKwargs. AddArgKwargs will support all of the keyword arguments of argparse's add_argument except for dest since that would conflict with the Tap class variable, which is automatically the destination for the argument.

We welcome any feedback and/or contributions.

Thanks,
--JK

[Daraan]

Hey I've just seen this. I think this looks nice and usable, Annotated works with other Annotated as nesting is flattened and also with type-checkers.