The purpose of duckargs is to save some typing whenever you want to quickly create a python program or C program that accepts command line arguments. Just run duckargs (generates python), duckargs-python (also generates python) or duckargs-c (generates C) with all the options/arguments that you want your program to accept, and duckargs will print the code for a program that handles those options/arguments.

If you're like me, then you often need to create little throwaway command-line tools, but not often enough to remember the exact syntax/details of argparse or getopt.h, so you often start these efforts by looking up the relevant docs and refreshing your memory.

Next, you spend some time typing out the boilerplate arg-parsing code, with one eye on the docs, and eventually (depending on how much arg-parsing boilerplate code you need) you may forget some interesting detail that was part of your original idea, or you may just get sick of it and decide that you don't event need a command-line tool, and you'll do the thing manually instead.

duckargs makes this process a little bit simpler, and shortens the time between your idea and having a working C or Python program.

Let's imagine that you want to create a little command-line tool that accepts the following command line options/arguments:

• A positional argument, string
• An optional integer value (-i or --intval)
• An optional float value (-f or --floatval)
• A flag (-q)

You can run duckargs and pass all those options/arguments/flags, and duckargs will generate a working program with all the boilerplate taken care of:

Generating Python

$ duckargs somestring -i --intval 99 -f --floatval 7.7 -q

Output

# Generated by duckargs, invoked with the following arguments:
# somestring -i --intval 99 -f --floatval 7.7 -q

import argparse

def main():
    parser = argparse.ArgumentParser(description='A command-line program generated by duckargs',
                                     formatter_class=argparse.ArgumentDefaultsHelpFormatter)

    parser.add_argument('somestring', help='a string')
    parser.add_argument('-i', '--intval', default=99, type=int, help='an int value')
    parser.add_argument('-f', '--floatval', default=7.7, type=float, help='a float value')
    parser.add_argument('-q', action='store_true', help='q flag')
    args = parser.parse_args()

    print(args.somestring)
    print(args.intval)
    print(args.floatval)
    print(args.q)

if __name__ == "__main__":
    main()

Generating C

$ duckargs-c somestring -i --intval 99 -f --floatval 7.7 -q

Output

// Generated by duckargs, invoked with the following arguments:
// somestring -i --intval 99 -f --floatval 7.7 -q

#include <stdbool.h>
#include <getopt.h>
#include <stdlib.h>
#include <stdio.h>

static char *somestring = "somestring";
static long int intval = 99;
static float floatval = 7.7;
static bool q = false;

static struct option long_options[] =
{
    {"intval", required_argument, NULL, 'i'},
    {"floatval", required_argument, NULL, 'f'},
    {NULL, 0, NULL, 0}
};

void print_usage(void)
{
    printf("\n");
    printf("USAGE:\n\n");
    printf("program_name [OPTIONS] somestring\n");
    printf("\nOPTIONS:\n\n");
    printf("-i --intval [int]      An int value (default: %ld)\n", int);
    printf("-f --floatval [float]  A float value (default: %.2f)\n", float);
    printf("-q                     A flag\n");
    printf("\n");
}

int parse_args(int argc, char *argv[])
{
    char *endptr = NULL;
    int ch;

    while ((ch = getopt_long(argc, argv, "i:f:q", long_options, NULL)) != -1)
    {
        switch (ch)
        {
            case 'i':
            {
                intval = strtol(optarg, &endptr, 0);
                if (endptr && (*endptr != '\0'))
                {
                    printf("Option '-i' requires an integer argument\n");
                    return -1;
                }
                break;
            }
            case 'f':
            {
                floatval = strtof(optarg, &endptr);
                if (endptr == optarg)
                {
                    printf("Option '-f' requires a floating-point argument\n");
                    return -1;
                }
                break;
            }
            case 'q':
            {
                q = true;
                break;
            }
        }
    }

    if (argc < (optind   1))
    {
        printf("Missing positional arguments\n");
        return -1;
    }

    somestring = argv[optind];

    return 0;
}

int main(int argc, char *argv[])
{
    if (argc < 2)
    {
        print_usage();
        return -1;
    }

    int ret = parse_args(argc, argv);
    if (0 != ret)
    {
        return ret;
    }

    printf("somestring: %s\n", somestring ? somestring : "null");
    printf("intval: %ld\n", intval);
    printf("floatval: %.4f\n", floatval);
    printf("q: %s\n", q ? "true" : "false");

    return 0;
}

Install with pip (python 3x required):

pip install duckargs

If you have an option which accepts an argument, and you write an argument string with multiple values separated by commas (e.g. -m --mode active,idle,sim), then generated python code will use the comma-separated values as a choices list for argparse:

parser.add_argument('-m', '--mode', choices=['active', 'idle', 'sim'], default='active', help='a string')

And generated C code will use the comma-separated values to restrict values in a similar manner:

static char *mode_choices[] = {"active", "idle", "stop"};
static char *mode = "active";

static struct option long_options[] =
{
    {"mode", required_argument, NULL, 'm'},
    {NULL, 0, NULL, 0}
};

void print_usage(void)
{
    printf("\n");
    printf("USAGE:\n\n");
    printf("program_name [OPTIONS]\n");
    printf("\nOPTIONS:\n\n");
    printf("-m --mode [active|idle|stop]  A string value (default: %s)\n", mode ? mode : "null");
    printf("\n");
}

int parse_args(int argc, char *argv[])
{
    int ch;

    while ((ch = getopt_long(argc, argv, "m:", long_options, NULL)) != -1)
    {
        switch (ch)
        {
            case 'm':
            {
                mode = optarg;
                for (int i = 0; i < 3; i  )
                {
                    if (0 == strcmp(mode_choices[i], mode))
                    {
                        break;
                    }
                    if (i == 2)
                    {
                        printf("Option '-m' must be one of ['active', 'idle', 'stop']\n");
                        return -1;
                    }
                }
                break;
            }
        }
    }

    return 0;
}

If you have an option that you want to accept a filename, you have two ways to tell duckargs that the option argument should be treated as a file:

• Pass the path to a file that actually exists (e.g. -f --filename file.txt) as the option argument
• Pass FILE as the option argument (e.g. -f --filename FILE)

Either of which will generate python code like this:

parser.add_argument('-f', '--filename', default='file', type=argparse.FileType(), help='a filename')

And will generate C code like this:

static char *filename = NULL;

static struct option long_options[] =
{
    {"filename", required_argument, NULL, 'f'},
    {NULL, 0, NULL, 0}
};

void print_usage(void)
{
    printf("\n");
    printf("USAGE:\n\n");
    printf("program_name [OPTIONS]\n");
    printf("\nOPTIONS:\n\n");
    printf("-f --filename FILE  A filename (default: %s)\n", filename ? filename : "null");
    printf("\n");
}

int parse_args(int argc, char *argv[])
{
    int ch;

    while ((ch = getopt_long(argc, argv, "f:", long_options, NULL)) != -1)
    {
        switch (ch)
        {
            case 'f':
            {
                filename = optarg;
                break;
            }
        }
    }

    return 0;
}

Some things can be configured by setting environment variables.

By default, duckargs generates a program that prints all provided arguments/options to stdout after argument parsing is complete. If you want to disable this and generate programs without the print statements, set DUCKARGS_PRINT=0 in your environment variables. This environment variable affects generated C code and generated python code.

By default, duckargs generates a program that prints a comment header at the top, showing the arguments that duckargs was invoked with. If you want to disable this and generate programs without the comment header, set DUCKARGS_COMMENT=0 in your environment variables. This environment variable affects generated C code and generated python code.

If you want to use duckargs in your own script, you can use the duckargs.generate_python_code and duckargs.generate_c_code functions, both of which accept a list of command line arguments:

import sys
from duckargs import generate_python_code, generate_c_code

python_code = generate_python_code(sys.argv)

c_code = generate_c_code(sys.argv)

If you have a combination of flags and positional arguments, and you happen to have a flag followed by a positional argument (as in: python -m duckargs -q --quiet positional_arg), duckargs has no way to tell that you wanted a positional arg, so it will assume you want an option -q --quiet with a required argument.

To avoid this, it is recommended to declare your positional arguments first (as in: python -m duckargs positional_arg -q --quiet)

Contributions are welcome, please open a pull request at https://github.com/eriknyquist/duckargs/pulls. You will need to install packages required for development by doing pip install -r dev_requirements.txt.

Please ensure that all existing tests pass, new test(s) are added if required, and the code coverage check passes.

• Run tests with python setup.py test.
• Run tests and and generate code coverage report with python code_coverage.py (this script will report an error if coverage is below 95%)

If you have any questions about / need help with contributions or tests, please contact Erik at [email protected].