How create an option with an optional argument (e.g. a flag with an optional value)

[taranlu-houzz]

First Check

• I added a very descriptive title here.
• I used the GitHub search to find a similar question and didn't find it.
• I searched the Typer documentation, with the integrated search.
• I already searched in Google "How to X in Typer" and didn't find any information.
• I already read and followed all the tutorial in the docs and didn't find an answer.
• I already checked if it is not related to Typer but to Click.

Commit to Help

• I commit to help with one of those options 👆

Example Code

from pprint import pprint as pp
from typing import Optional
import typer


APP = typer.Typer(
    rich_markup_mode="markdown",
    pretty_exceptions_show_locals=False,
)


@APP.command()
def test(
    opt_1: Optional[float] = typer.Option(
        None,
        "--opt-1",
        is_flag=False,
        flag_value=3.14,
        help="blah blah",
    ),
) -> None:
    pp(locals())


if __name__ == "__main__":
    APP()

Description

In click, it is possible to create an option with an optional value: https://click.palletsprojects.com/en/8.1.x/options/#optional-value

I'm wondering if it is possible to do this in typer?

For the example given above, I would expect the following:

• No --opt-1 flag passed: None
• --opt-1 flag is passed with no value: 3.14 (default value)
• --opt-1 flag is passed with a value (99): 99 (value that was passed)

Operating System

macOS

Operating System Details

No response

Typer Version

0.9.0

Python Version

3.10.10

Additional Context

No response

[e-sr]

some hints? how to do this?
I tried like in clik docs:

@app.command()
def test_flag(flag: Optional[str] = typer.Option(None, is_flag=False, flag_value='default')):
    if flag is not None:
        print(f"{flag=}")
    else:
        print("flag unset")

calling
app test-flag is ok
app test-flag --flag is ok
app test-flag --flag=nodefault raise an exception

Option '--flag' does not take a value.                                                                                           │

what is the purpose of parameter is_flag

[MartinSoto]

Any appropriate answers to this question? This kind of behavior is common in CLI programs, which is the reason why Click supports it.

This kind of thing makes Typer inadequate for everything but the simplest CLI programs. Really sad given that the general concept of it is very good.

[davidwaroquiers]

Also wondering how to do this. I've been trying different ways and none of them worked.