Define optional argument with exactly 1 value, + default value

[nmoreaud]

Hello,

I try to define an optional parameter with a value + default value, but it doesn't work as I expect. I use version 3.0.

What I'd like to obtain:

• Optional [] in usage section: Usage: [--format1 VAR] --format2 VAR --format3 VAR [--format4 VAR] ok for format1 and format4
• Exception if argument is called without value: ok for --format2 and --format3
• No mention of [nargs=0..1] in argument section:

  --format1                  Image format [jpg|png] [nargs=0..1] [default: "jpg"]
  --format2                  Image format r1 [jpg|png] [default: "jpg"]                            => ok
  --format3                  Image format r [jpg|png] [nargs=0..1] [default: "jpg"]
  --format4                  Image format 1 [jpg|png] [default: "jpg"]                             => ok

• No mention of [required] in argument section: ok for all
• Listed in "Optional arguments" section: ok for all

Could you help me?

Here is a sample program:

        command.add_argument("--format1")
            .default_value(string("jpg"))
            .help("Image format [jpg|png]");

        command.add_argument("--format2")
            .default_value(string("jpg"))
            .required()
            .nargs(1)
            .help("Image format r1 [jpg|png]");

        command.add_argument("--format3")
            .default_value(string("jpg"))
            .required()
            .help("Image format r [jpg|png]");

        command.add_argument("--format4")
            .default_value(string("jpg"))
            .nargs(1)
            .help("Image format 1 [jpg|png]");

[Eng-MohamedHussien]

• I suggest reading README, it has answers of all your questions.

[Eng-MohamedHussien]

Let's discuss sample program:

command.add_argument("--format1")
            .default_value(string("jpg"))
            .help("Image format [jpg|png]");

• If you didn't provide that argument, no exception will be fired as you provided a default value.
• --help output:

  --format1      Image format [jpg|png] [nargs=0..1] [default: "jpg"]

  • You can do the same for argument --format4.

[Eng-MohamedHussien]

• --format2 & --format3 are same.

  command.add_argument("--format3")
          .default_value(string("jpg"))
          .required()
          .help("Image format r [jpg|png]");

• By adding here default_value you lost the exception that will be fired when no argument is passed (Read previous mentioned section).

[Eng-MohamedHussien]

• Correct version:

  
  command.add_argument("--format1")
  .default_value(string("jpg"))
  .help("Image format [jpg|png]");

command.add_argument("--format2") .required() .help("Image format [jpg|png]");

command.add_argument("--format3") .required() .help("Image format [jpg|png]");

command.add_argument("--format4") .default_value(string("jpg")) .help("Image format [jpg|png]");

- Help output:
![Screenshot from 2024-08-27 20-42-07](https://github.com/user-attachments/assets/2c066aed-fb6e-4105-9565-9c5cb3130500)

[Eng-MohamedHussien]

@nmoreaud, If you don't have extra questions, kindly close the ticket.

[Eng-MohamedHussien]

@p-ranav, Kindly close the ticket.

[nmoreaud]

Hello I cannot test now, but I don't really see an answer to my question. Basically you recommend to use either "default" or "required" and none of these two syntaxes seem to address every point of the question. The 4 syntaxes in the ticket description are 4 attempts to address every point of the question, and none of them is correct. But you can also close the ticket as "by design".