A simple utility function for enforcing mutual exclusivity between click options.

example_usage.sh

$ python single_context_mutually_exclusive.py -a
$ python single_context_mutually_exclusive.py -b
$ python single_context_mutually_exclusive.py -a -b
Usage: single_context_mutually_exclusive.py [OPTIONS]
Error: options a, b, and c are mutually exclusive
$ python single_context_mutually_exclusive.py -b -c
Usage: single_context_mutually_exclusive.py [OPTIONS]
Error: options a, b, and c are mutually exclusive
$ python single_context_mutually_exclusive.py -a -b -c
Usage: single_context_mutually_exclusive.py [OPTIONS]
Error: options a, b, and c are mutually exclusive
$ python multiple_context_mutually_exclusive.py -a
$ python multiple_context_mutually_exclusive.py -a command -b
Usage: multiple_context_mutually_exclusive.py.py command [OPTIONS]
Error: command option b may not be specified with application option a
$ python multiple_context_mutually_exclusive.py -a command -c
$ python multiple_context_mutually_exclusive.py command -c -d
$ python multiple_context_mutually_exclusive.py command -b -c
Usage: multiple_context_mutually_exclusive.py.py command [OPTIONS]
Error: command option c may not be specified with command option b

multiple_context_mutually_exclusive.py

import click

def exclusive(ctx_params, exclusive_params, error_message):
    if sum([1 if ctx_params[p] else 0 for p in exclusive_params]) > 1:
        raise click.UsageError(error_message)

@click.group()
@click.option('-a', is_flag=True)
@click.pass_context
def cli(ctx, a):
    pass

@cli.command()
@click.option('-b', is_flag=True)
@click.option('-c', is_flag=True)
@click.option('-d', is_flag=True)
@click.pass_context
def command(ctx, b, c, d):
    exclusive(ctx.params, ['b', 'c'], 'command option c may not be specified with command option b')
    exclusive(ctx.params, ['b', 'd'], 'command option d may not be specified with command option b')
    exclusive({**ctx.params, **ctx.parent.params}, ['a', 'b'], 'command option b may not be specified with application option a')
    """
    Note: {**ctx.params, **ctx.parent.params} is a python3.5+ idiom for merging dictionaries. If you are using a previous version, you can do something like:
    ctx_params = ctx.params.copy()
    ctx_params.update(ctx.parent.params)
    then pass ctx_params dictionary to exclusive()
    Also Note:
    Since dictionaries retain the last-defined value for each key, this function will be unreliable or non-functional if you reuse option names in different contexts.
    """

if __name__ == '__main__':
    cli()

single_context_mutually_exclusive.py

import click

def exclusive(ctx_params, exclusive_params, error_message):
    if sum([1 if ctx_params[p] else 0 for p in exclusive_params]) > 1:
        raise click.UsageError(error_message)

@click.command()
@click.option('-a', is_flag=True)
@click.option('-b', is_flag=True)
@click.option('-c', is_flag=True)
def example_command(a, b, c):
    exclusive(click.get_current_context().params, ['a', 'b', 'c'], 'options a, b, and c are mutually exclusive')

if __name__ == '__main__':
    example_command()