CLI Parameter Types

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 3.9+

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:

$ python main.py --help

// Notice how --age is an INTEGER and --height-meters is a FLOAT
Usage: main.py [OPTIONS] NAME

Arguments:
  NAME  [required]

Options:
  --age INTEGER           [default: 20]
  --height-meters FLOAT   [default: 1.89]
  --female / --no-female  [default: True]
  --help                  Show this message and exit.

// Call it with CLI parameters
$ 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
$ python main.py Camila --age 15.3

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

Error: Invalid value for '--age': '15.3' is not a valid integer

// Because 15.3 is not an INTEGER (it's a float)

Watch next

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