Allow env variable only

[vk496]

import typer
from typing import Annotated


def main(name: Annotated[str, typer.Option(..., envvar="NAME")]):
    print(f"Hello {name}")


if __name__ == "__main__":
    typer.run(main)

Hello,

I have a app that use threads/processes under the hood, so any initialized variables passed from args is not propagated/saved in the newly created process. However, ENV vars are accessible from there.

I know that ENV vars are a alternative way. But can they be the ONLY way to define arguments?
Operating System

Linux
Operating System Details

No response
Typer Version

0.15.1
Python Version

3.12.8
Additional Context

No response

[kinuax]

Yes, there is a way to only allow parameters initialized from environment variables leveraging Click's Context and ParameterSource.

Solution:

import typer
from click.core import ParameterSource
from typing import Annotated

def allow_only_env_var(ctx: typer.Context, param: typer.CallbackParam, value: str) -> str:
    if ctx.get_parameter_source(param.name) != ParameterSource.ENVIRONMENT:
        raise typer.BadParameter("only allowed as env var.")
    return value

def main(name: Annotated[str, typer.Option(envvar="NAME", callback=allow_only_env_var)]):
    print(f"Hello {name}")

if __name__ == "__main__":
    typer.run(main)

Behavior:

$ python cli.py
Usage: cli.py [OPTIONS]
Try 'cli.py --help' for help.
╭─ Error ────────────────────────────────────╮
│ Missing option '--name' (env var: 'NAME'). │
╰────────────────────────────────────────────╯

$ python cli.py --name FOO
Usage: cli.py [OPTIONS]
Try 'cli.py --help' for help.
╭─ Error ────────────────────────────────────────────╮
│ Invalid value for '--name' (env var: 'NAME'): only │
│ allowed as an env var.                             │
╰────────────────────────────────────────────────────╯

$ NAME=BAR python cli.py --name FOO
Usage: cli.py [OPTIONS]
Try 'cli.py --help' for help.
╭─ Error ────────────────────────────────────────────╮
│ Invalid value for '--name' (env var: 'NAME'): only │
│ allowed as an env var.                             │
╰────────────────────────────────────────────────────╯

$ NAME=BAR python cli.py
Hello BAR