Usage

The Prompt class

The simplest way to use promptpy is to create an instance of the Prompt class, and use the methods to get and validate command line input:

from promptpy import Prompt

prompt = Prompt()
prompt.integer("Pick a number", min=1, max=10, default=7)

This will display the command line prompt:

Pick a number (1-10) [7]:

Input will be validated and the method will reprompt if necessary, displaying context-specific error messages until a valid integer is entered.

Methods

Prompt ships with a variety of methods to prompt for and validate different types of data:

• date() prompt for a date

• float() prompt for a floating point decimal number

• integer() prompt for an integer

• list() prompt for a list of strings, separated by commas

• options() prompt for one of a set of single-character options

• yes_no() prompt for yes or no

Validators

All the above methods call the prompt() method under the hood. This method takes a list of Validators which validate the text entered at the command line.

A Validator is a callable which takes a string as its sole parameter and raises a ValidationError if validation fails, or returns None.

promptpy ships with a range of validators covering integers, floating point numbers, etc. - see validators for more detail.

You can easily extend prompt functionality by creating your own validators. For example, the following creates a validator and prompt that will only accept prime numbers:

from promptpy import Prompt
from promptpy.validators import IntegerValidator, ValidationError

class PrimeValidator(IntegerValidator):
    """Validates that a string represents a prime number."""

    def __init__(self):
        super().__init__(min=2)

    def __call__(self, text: str) -> None:
        """Validate a string.

        Validates that the string represents a prime number
        and raises a :exc:`ValidationError` if it doesn't.

        :param text: string to validate
        :type text: str
        :raises: :exc:`ValidationError` if validation fails
        """
        # Check this is an integer 2 or greater
        super().__call__(text)

        # Check this is a prime number
        n = int(text)
        for i in range(2, int(n ** 0.5) + 1):
            if n % i == 0:
                raise ValidationError("{} is not a prime number".format(n))

def get_prime():
    """Prompt for a prime number"""
    validator = PrimeValidator()
    prompt = Prompt()
    prime = prompt.prompt("Please enter a prime number", validators=[validator])
    print(f"You entered {prime}.")

Rich

promptpy uses the Rich library to provide pretty command-line output.

If you have a Rich Console instance already in your application you should supply it to the Prompt constructor. Otherwise the constructor will create and use its own instance.