Boolean CLI Options

We have seen some examples of CLI options with bool, and how Typer creates --something and --no-something automatically.

But we can customize those names.

Only --force

Let's say that we want a --force CLI option only, we want to discard --no-force.

We can do that by specifying the exact name we want:

Python 3.8+

import typer
from typing_extensions import Annotated


def main(force: Annotated[bool, typer.Option("--force")] = False):
    if force:
        print("Forcing operation")
    else:
        print("Not forcing")


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

🤓 Other versions and variants

Python 3.8+ - non-Annotated

Tip

Prefer to use the Annotated version if possible.

import typer


def main(force: bool = typer.Option(False, "--force")):
    if force:
        print("Forcing operation")
    else:
        print("Not forcing")


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

Now there's only a --force CLI option:

// Check the help
$ python main.py --help

// Notice there's only --force, we no longer have --no-force
Usage: main.py [OPTIONS]

Options:
  --force               [default: False]
  --help                Show this message and exit.

// Try it:
$ python main.py

Not forcing

// Now add --force
$ python main.py --force

Forcing operation

// And --no-force no longer exists ⛔️
$ python main.py --no-force

Usage: main.py [OPTIONS]
Try "main.py --help" for help.

Error: No such option: --no-force

Alternative names

Now let's imagine we have a CLI option --accept.

And we want to allow setting --accept or the contrary, but --no-accept looks ugly.

We might want to instead have --accept and --reject.

We can do that by passing a single str with the 2 names for the bool CLI option separated by /:

Python 3.8+

from typing import Optional

import typer
from typing_extensions import Annotated


def main(accept: Annotated[Optional[bool], typer.Option("--accept/--reject")] = None):
    if accept is None:
        print("I don't know what you want yet")
    elif accept:
        print("Accepting!")
    else:
        print("Rejecting!")


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

🤓 Other versions and variants

Python 3.8+ - non-Annotated

Tip

Prefer to use the Annotated version if possible.

from typing import Optional

import typer


def main(accept: Optional[bool] = typer.Option(None, "--accept/--reject")):
    if accept is None:
        print("I don't know what you want yet")
    elif accept:
        print("Accepting!")
    else:
        print("Rejecting!")


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

Check it:

// Check the help
$ python main.py --help

// Notice the --accept / --reject
Usage: main.py [OPTIONS]

Options:
  --accept / --reject
  --help                Show this message and exit.

// Try it
$ python main.py

I don't know what you want yet

// Now pass --accept
$ python main.py --accept

Accepting!

// And --reject
$ python main.py --reject

Rejecting!

Short names

The same way, you can declare short versions of the names for these CLI options.

For example, let's say we want -f for --force and -F for --no-force:

Python 3.8+

import typer
from typing_extensions import Annotated


def main(force: Annotated[bool, typer.Option("--force/--no-force", "-f/-F")] = False):
    if force:
        print("Forcing operation")
    else:
        print("Not forcing")


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

🤓 Other versions and variants

Python 3.8+ - non-Annotated

Tip

Prefer to use the Annotated version if possible.

import typer


def main(force: bool = typer.Option(False, "--force/--no-force", "-f/-F")):
    if force:
        print("Forcing operation")
    else:
        print("Not forcing")


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

Check it:

// Check the help
$ python main.py --help

// Notice the -f, --force / -F, --no-force
Usage: main.py [OPTIONS]

Options:
  -f, --force / -F, --no-force  [default: False]
  --help                        Show this message and exit.

// Try with the short name -f
$ python main.py -f

Forcing operation

// Try with the short name -F
$ python main.py -F

Not forcing

Only names for False

If you want to (although it might not be a good idea), you can declare only CLI option names to set the False value.

To do that, use a space and a single / and pass the negative name after:

Python 3.8+

import typer
from typing_extensions import Annotated


def main(in_prod: Annotated[bool, typer.Option(" /--demo", " /-d")] = True):
    if in_prod:
        print("Running in production")
    else:
        print("Running demo")


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

🤓 Other versions and variants

Python 3.8+ - non-Annotated

Tip

Prefer to use the Annotated version if possible.

import typer


def main(in_prod: bool = typer.Option(True, " /--demo", " /-d")):
    if in_prod:
        print("Running in production")
    else:
        print("Running demo")


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

Tip

Have in mind that it's a string with a preceding space and then a /.

So, it's " /-S" not "/-S".

Check it:

// Check the help
$ python main.py --help

// Notice the / -d, --demo
Usage: main.py [OPTIONS]

Options:
   / -d, --demo         [default: True]
  --help                Show this message and exit.

// Try it
$ python main.py

Running in production

// Now pass --demo
$ python main.py --demo

Running demo

// And the short version
$ python main.py -d

Running demo