Creating a Click.Option with prompt that shows only if default value is empty

Question

Given the following option:

@cli.command()
@click.option('--param', default=lambda: get_value(), prompt="Enter Param")

Normal behavior is for click to show a prompt to enter a value for param and display the default value (and you can just ENTER through it to preserve that).

Instead I'd like the param prompt to only show if get_value() returns None or some pre-defined "show" value, but for any Truthy/Other value for get_value() click will not show the prompt for this option and run the command or move to the next prompt.

Answer 1

This can be done by over riding the click.Option.get_default() and the click.Option.prompt_for_value() methods like:

Custom Class:

import click

class OptionPromptNull(click.Option):
    _value_key = '_default_val'

    def get_default(self, ctx):
        if not hasattr(self, self._value_key):
            default = super(OptionPromptNull, self).get_default(ctx)
            setattr(self, self._value_key, default)
        return getattr(self, self._value_key)

    def prompt_for_value(self, ctx):        
        default = self.get_default(ctx)

        # only prompt if the default value is None
        if default is None:
            return super(OptionPromptNull, self).prompt_for_value(ctx)

        return default

Using Custom Class:

Then to use the custom class, pass it as the cls argument to the option decorator like:

@click.command()
@click.option('--param', cls=OptionPromptNull,
              default=lambda: get_value(), prompt="Enter Param")
def cli(param):
    click.echo("param: '{}'".format(param))

Test Code:

@click.command()
@click.option('--param1', cls=OptionPromptNull,
              default=lambda: get_value_none(), prompt="Enter Param1")
@click.option('--param2', cls=OptionPromptNull,
              default=lambda: get_value_one(), prompt="Enter Param2")
def cli(param1, param2):
    click.echo("param1: '{}'".format(param1))
    click.echo("param2: '{}'".format(param2))


def get_value_none():
    return None

def get_value_one():
    return 1

cli([])

Result:

Enter Param1: 23
param1: '23'
param2: '1'