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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.

!!! note

Boolean options may behave slightly differently from other parameter types.
When using a single flag (for example, only `--force` without a `--no-force`
counterpart), the default value might not be shown in the `--help` output
for single boolean flags.

This behavior comes from Click and is expected, even though the actual
default value is still correctly applied.

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

from typing import Annotated

import typer

app = typer.Typer()


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


if __name__ == "__main__":
    app()
🤓 Other versions and variants

Tip

Prefer to use the Annotated version if possible.

import typer

app = typer.Typer()


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


if __name__ == "__main__":
    app()

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 /:

from typing import Annotated

import typer

app = typer.Typer()


@app.command()
def main(accept: Annotated[bool | None, 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__":
    app()
🤓 Other versions and variants

Tip

Prefer to use the Annotated version if possible.

import typer

app = typer.Typer()


@app.command()
def main(accept: bool | None = 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__":
    app()

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:

from typing import Annotated

import typer

app = typer.Typer()


@app.command()
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__":
    app()
🤓 Other versions and variants

Tip

Prefer to use the Annotated version if possible.

import typer

app = typer.Typer()


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


if __name__ == "__main__":
    app()

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:

from typing import Annotated

import typer

app = typer.Typer()


@app.command()
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__":
    app()
🤓 Other versions and variants

Tip

Prefer to use the Annotated version if possible.

import typer

app = typer.Typer()


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


if __name__ == "__main__":
    app()

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