Error: Got unexpected extra arguments when using Click library

The way you've written your code, you shouldn't be defined hello1 and hello2 as commands. If you simply remove the decorator, your code works as written. That is, given:

import click

@click.group(name='script')
def cli():
    pass

def hello1():
    click.echo('Hello, World!')

def hello2():
    click.echo('Hola, Mundo!')

@cli.command()
@click.argument('function', type=click.Choice(['hello1', 'hello2']))
def hello(function):
    if function == 'hello1':
        hello1()
    elif function == 'hello2':
        hello2()

if __name__ == '__main__':
    cli()

We can run:

$ python script.py hello hello1
Hello, World!
$ python script.py hello hello2
Hola, Mundo!

If you want hello1 and hello2 to be subcommands of hello, then you would need to redefine hello as a command group, like this:

import click

@click.group(name='script')
def cli():
    pass

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

@hello.command()
def hello1():
    click.echo('Hello, World!')

@hello.command()
def hello2():
    click.echo('Hola, Mundo!')


if __name__ == '__main__':
    cli()

This supports the same command lines, but instead of explicitly testing for an argument we rely on click to dispatch the appropriate command.