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Number

You can define numeric validations with max and min values for int and float CLI parameters:

import typer


def main(
    id: int = typer.Argument(..., min=0, max=1000),
    age: int = typer.Option(20, min=18),
    score: float = typer.Option(0, max=100),
):
    typer.echo(f"ID is {id}")
    typer.echo(f"--age is {age}")
    typer.echo(f"--score is {score}")


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

CLI arguments and CLI options can both use these validations.

You can specify min, max or both.

Check it:

$ python main.py --help

// Notice the extra RANGE in the help text for --age and --score
Usage: main.py [OPTIONS] ID

Arguments:
  ID  [required]

Options:
  --age INTEGER RANGE   [default: 20]
  --score FLOAT RANGE   [default: 0]
  --install-completion  Install completion for the current shell.
  --show-completion     Show completion for the current shell, to copy it or customize the installation.
  --help                Show this message and exit.

// Pass all the CLI parameters
$ python main.py 5 --age 20 --score 90

ID is 5
--age is 20
--score is 90.0

// Pass an invalid ID
$ python main.py 1002

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

Error: Invalid value for 'ID': 1002 is not in the valid range of 0 to 1000.

// Pass an invalid age
$ python main.py 5 --age 15

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

Error: Invalid value for '--age': 15 is smaller than the minimum valid value 18.

// Pass an invalid score
$ python main.py 5 --age 20 --score 100.5

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

Error: Invalid value for '--score': 100.5 is bigger than the maximum valid value 100.

// But as we didn't specify a minimum score, this is accepted
$ python main.py 5 --age 20 --score -5

ID is 5
--age is 20
--score is -5.0

Clamping numbers

You might want to, instead of showing an error, use the closest minimum or maximum valid values.

You can do it with the clamp parameter:

import typer


def main(
    id: int = typer.Argument(..., min=0, max=1000),
    rank: int = typer.Option(0, max=10, clamp=True),
    score: float = typer.Option(0, min=0, max=100, clamp=True),
):
    typer.echo(f"ID is {id}")
    typer.echo(f"--rank is {rank}")
    typer.echo(f"--score is {score}")


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

And then, when you pass data that is out of the valid range, it will be "clamped", the closest valid value will be used:

// ID doesn't have clamp, so it shows an error
$ python main.py 1002

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

Error: Invalid value for 'ID': 1002 is not in the valid range of 0 to 1000.

// But --rank and --score use clamp
$ python main.py 5 --rank 11 --score -5

ID is 5
--rank is 10
--score is 0

Counter CLI options

You can make a CLI option work as a counter with the counter parameter:

import typer


def main(verbose: int = typer.Option(0, "--verbose", "-v", count=True)):
    typer.echo(f"Verbose level is {verbose}")


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

It means that the CLI option will be like a boolean flag, e.g. --verbose.

And the value you receive in the function will be the amount of times that --verbose was added:

// Check it
$ python main.py

Verbose level is 0

// Now use one --verbose
$ python main.py --verbose

Verbose level is 1

// Now 3 --verbose
$ python main.py --verbose --verbose --verbose

Verbose level is 3

// And with the short name
$ python main.py -v

Verbose level is 1

// And with the short name 3 times
$ python main.py -v -v -v

Verbose level is 3

// As short names can be put together, this also works
$ python main.py -vvv

Verbose level is 3