pythoncommand-line-interfaceargparse

Dynamic argument types in Python + argparse

I want to create a CLI using Python and argparse. The CLI should have options to specify a list of values, and also to dynamically specify the type of the values (str, int, float, etc.) in that list (all arguments in the list have the same type). The values in the list must be converted to the specified type.

I have the following baseline implementation, which does work, but if feels a bit clunky, especially when adding more complex types (or even functions which process the input list of arguments). I was wondering if there is a built-in/smoother/more canonical way to do this?

script.py:

import argparse

arg_type_dict = {t.__name__: t for t in [str, int, float]}

def main(
    sweep_arg_type: str,
    sweep_arg_vals: list,
):
    arg_type = arg_type_dict[sweep_arg_type]
    val_list = [arg_type(val_str) for val_str in sweep_arg_vals]

    print(val_list)

if __name__ == "__main__":
    parser = argparse.ArgumentParser()
    parser.add_argument("--sweep_arg_vals", required=True, nargs="+")
    parser.add_argument(
        "--sweep_arg_type",
        required=True,
        choices=sorted(arg_type_dict.keys()),
    )
    args = parser.parse_args()

    main(
        args.sweep_arg_type,
        args.sweep_arg_vals,
    )

Usage examples:

python script.py -h
python script.py --sweep_arg_type int    --sweep_arg_vals 0 1 10 -3
python script.py --sweep_arg_type float  --sweep_arg_vals 0 1 10 -3
python script.py --sweep_arg_type float  --sweep_arg_vals 1.2 3.4
python script.py --sweep_arg_type str    --sweep_arg_vals abc def lmnop
Solution

  • I believe the second option in your own solution is the simplest to implement. Note that the arguments are simply JSON values.

    import argparse
import json


def main():
    parser = argparse.ArgumentParser()
    parser.add_argument("--sweep_arg_vals", required=True, type=json.loads)
    args = parser.parse_args()
    print(args.sweep_arg_vals)


if __name__ == "__main__":
    main()

    Sample runs

    python3 my.py --sweep_arg_vals '[0, 1, 10, -3]'
[0, 1, 10, -3]

python3 my.py --sweep_arg_vals '[1.1, 1.2]'
[1.1, 1.2]

python3 my.py --sweep_arg_vals '["abc", "def", "lmnop"]'
['abc', 'def', 'lmnop']

    Notes