CLI Parameter Types¶

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Use the official Typer skill for your installed version. Install it from your project directory:

uvx library-skills

See Develop with AI.

You can use several data types for the CLI options and CLI arguments, and you can add data validation requirements too.

Data conversion¶

When you declare a CLI parameter with some type Typer will convert the data received in the command line to that data type.

For example:

Python 3.10+

import typer

app = typer.Typer()


@app.command()
def main(name: str, age: int = 20, height_meters: float = 1.89, female: bool = True):
    print(f"NAME is {name}, of type: {type(name)}")
    print(f"--age is {age}, of type: {type(age)}")
    print(f"--height-meters is {height_meters}, of type: {type(height_meters)}")
    print(f"--female is {female}, of type: {type(female)}")


if __name__ == "__main__":
    app()

In this example, the value received for the CLI argument name will be treated as str.

The value for the CLI option --age will be converted to an int and --height-meters will be converted to a float.

And as female is a bool CLI option, Typer will convert it to a "flag" --female and the counterpart --no-female.

And here's how it looks like:

$ uv run python main.py --help

// Notice how --age is an 'int' (integer) and --height-meters is a 'float'
Usage: main.py [OPTIONS] {name}

Arguments:
  name <str>  [required]

Options:
  --age <int>               [default: 20]
  --height-meters <float>   [default: 1.89]
  --female / --no-female    [default: female]
  --help                    Show this message and exit.

// Call it with CLI parameters
$ uv run python main.py Camila --age 15 --height-meters 1.70 --female

// All the data has the correct Python type
name is Camila, of type: <class 'str'>
--age is 15, of type: <class 'int'>
--height-meters is 1.7, of type: <class 'float'>
--female is True, of type: <class 'bool'>

// And if you pass an incorrect type
$ uv run python main.py Camila --age 15.3

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

Error: Invalid value for '--age': Input should be a valid integer, unable to parse string as an integer

// Because 15.3 is not an integer.

Watch next¶

See more about specific types and validations in the next sections...