Simple argument parser

simple_argument_parser.py

#!/usr/bin/python3
# Requires Python 3.7+ or CPython 3.6 for ordered dict
# Lightweight type-checking argument parser requiring minimal boilerplate
# Just a coding exercise for myself, but if you like it please use it!
# Todo:
#   - Boolean flags and grouping (e.g. "-o -a", "-xAd")
#   - Required and optional arguments (e.g. "--mode quiet -n 2")

import sys
from collections import namedtuple


def _print_error(message):
    print("{} : error :".format(sys.argv[0].split("/")[-1]), message)


def _print_usage(argument_spec):
    arg_usage_template = " {}" * len(argument_spec)
    arguments_string = arg_usage_template.format(*argument_spec.keys())
    print("Usage: python {}".format(sys.argv[0].split("/")[-1]) + arguments_string)
    type_hint_template = "\t{{}}:\t{}\n" * len(argument_spec)
    print(type_hint_template.format(*(func.__name__ for func in argument_spec.values())).format(*argument_spec.keys()))
    sys.exit(1)


def parse_args(argument_spec):
    """
    Provide an argument specification as a dictionary. The keys are named arguments, in order, with the values as their typ
    """
    if len(sys.argv) > 1 and sys.argv[1] == "--help":
        _print_usage(argument_spec)
    if len(sys.argv) != len(argument_spec) + 1:
        _print_error("{} arguments expected, {} given".format(len(argument_spec), len(sys.argv) - 1))
        _print_usage(argument_spec)
    try:
        named_args = dict(zip(argument_spec.keys(), sys.argv[1:]))
        typed_args = (arg_func(named_args[arg]) for arg, arg_func in argument_spec.items())
        return namedtuple("Arguments", argument_spec.keys())(*typed_args)
    except ValueError as e:
        _print_error(e)
        _print_usage(argument_spec)


if __name__ == "__main__":
    # usage/test/demo
    sample_argument_spec = {
        "something": str,
        "some_number": int,
        "another_number": float
    }
    args = parse_args(sample_argument_spec)
    
    print(args.something)
    print(args.some_number)
    print(args.another_number)