Add to_argv utility function that constructs an argv list.

[carlosgmartin]

Fixes #186.

[martinjm97]

Hi @carlosgmartin,

Thank you for this PR!

Our key concern is that it is often challenging to automatically reconstruct the argument list from an object instance. For example,

from tap import Tap


class Args(Tap):
    number: int

    def configure(self) -> None:
        self.add_argument("--number", type=lambda value: int(value) + 1)

The original argument is parsed as follows:

args = Args().parse_args(["--number", "1"])
assert args.number == 2

to_argv(args) would stringify the resulting value:

argv = to_argv(args)
assert argv == ["--number", "2"]

Reparsing those arguments changes the value again:

reparsed = Args().parse_args(argv)
assert reparsed.number == 3

Therefore:

assert args.as_dict() != reparsed.as_dict()

Tap and argparse do not require an argument’s type converter to satisfy type_converter(str(value)) == value, so to_argv() cannot generally guarantee a lossless round trip.

More generally, it is challenging to support custom actions, subparsers, complex nargs, duplicate destinations, and other configurations whose final values do not uniquely determine a valid list[str] input.

We will leave this issue open for a few weeks for potential further discussion.

Thanks again and we wish you happy Tapping,
JK