import click
import os


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


def get_env_vars(ctx, args, incomplete):
    # Completions returned as strings do not have a description displayed.
    for key in os.environ.keys():
        if incomplete in key:
            yield key


@cli.command(help='A command to print environment variables')
@click.argument("envvar", type=click.STRING, autocompletion=get_env_vars)
def cmd1(envvar):
    click.echo('Environment variable: %s' % envvar)
    click.echo('Value: %s' % os.environ[envvar])


@click.group(help='A group that holds a subcommand')
def group():
    pass


def list_users(ctx, args, incomplete):
    # You can generate completions with descriptions by returning
    # tuples in the form (completion, description).
    users = [('bob', 'butcher'),
             ('alice', 'baker'),
             ('jerry', 'candlestick maker')]
    # Ths will allow completion matches based on matches within the description string too!
    return [user for user in users if incomplete in user[0] or incomplete in user[1]]


@group.command(help='Choose a user')
@click.argument("user", type=click.STRING, autocompletion=list_users)
def subcmd(user):
    click.echo('Chosen user is %s' % user)


cli.add_command(group)