Using Boolean Flags in Python Click Library (command line arguments)

Question

I'm trying to make a verbose flag for my Python program. Currently, I'm doing this:

import click

#global variable
verboseFlag = False

#parse arguments
@click.command()
@click.option('--verbose', '-v', is_flag=True, help="Print more output.")
def log(verbose):
    global verboseFlag
    verboseFlag = True

def main():    
    log()        
    if verboseFlag:
         print("Verbose on!")

if __name__ == "__main__":
    main()

It'll never print "Verbose on!" even when I set the '-v' argument. My thoughts are that the log function needs a parameter, but what do I give it? Also, is there a way to check whether the verbose flag is on without global variables?

Answer 1

So click is not simply a command line parser. It also dispatches and processes the commands. So in your example, the log() function never returns to main() . The intention of the framework is that the decorated function, ie: log() , will do the needed work.

Code:

import click

@click.command()
@click.option('--verbose', '-v', is_flag=True, help="Print more output.")
def log(verbose):
    click.echo("Verbose {}!".format('on' if verbose else 'off'))


def main(*args):
    log(*args)

Test Code:

if __name__ == "__main__":
    commands = (
        '--verbose',
        '-v',
        '',
        '--help',
    )

    import sys, time

    time.sleep(1)
    print('Click Version: {}'.format(click.__version__))
    print('Python Version: {}'.format(sys.version))
    for cmd in commands:
        try:
            time.sleep(0.1)
            print('-----------')
            print('> ' + cmd)
            time.sleep(0.1)
            main(cmd.split())

        except BaseException as exc:
            if str(exc) != '0' and \
                    not isinstance(exc, (click.ClickException, SystemExit)):
                raise

Results:

Click Version: 6.7
Python Version: 3.6.3 (v3.6.3:2c5fed8, Oct  3 2017, 18:11:49) [MSC v.1900 64 bit (AMD64)]
-----------
> --verbose
Verbose on!
-----------
> -v
Verbose on!
-----------
> 
Verbose off!
-----------
> --help
Usage: test.py [OPTIONS]

Options:
  -v, --verbose  Print more output.
  --help         Show this message and exit.

Answer 2

The above answer was helpful, but this is what I ended up using. I thought I'd share since so many people are looking at this question:

@click.command()
@click.option('--verbose', '-v', is_flag=True, help="Print more output.")
def main(verbose):
    if verbose:
        # do something

if __name__ == "__main__":
    # pylint: disable=no-value-for-parameter
    main()