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?

Wiseman

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.

Pitsaw

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()

Wiseman