dev-notes/python/libs/cli/click.md

Click Lib

Command Creation

import click

# the decorator converts the function into a Command which then can be invoked
@click.command()
def hello():
    click.echo('Hello World!')

if __name__ == '__main__':
    hello()

Nesting Commands

Commands can be attached to other commands of type Group. This allows arbitrary nesting of scripts. As an example here is a script that implements two commands for managing databases:

@click.group()
def cli():
    pass

@click.command()
def initdb():
    click.echo('Initialized the database')

@click.command()
def dropdb():
    click.echo('Dropped the database')

cli.add_command(initdb)
cli.add_command(dropdb)

The group() decorator works like the command() decorator, but creates a Group object instead which can be given multiple subcommands that can be attached with Group.add_command().

For simple scripts, it's also possible to automatically attach and create a command by using the Group.command() decorator instead.
The above script can instead be written like this:

@click.group()
def cli():
    pass

@cli.command()
def initdb():
    click.echo('Initialized the database')

@cli.command()
def dropdb():
    click.echo('Dropped the database')

You would then invoke the Group in your setup-tools entry points or other invocations:

if __name__ == '__main__':
    cli()

Adding Parameters

To add parameters, use the option() and argument() decorators:

@click.command()
@click.option('--count', default=1, help='number of greetings')
@click.argument('name')
def hello(count, name):
    for x in range(count):
        click.echo(f'Hello {name}!')