How do I know if flag was passed by the user or has default value?

Sample code:

import click

@click.command
@click.option('-f/-F', 'var', default=True)
def main(var):
    click.echo(var)

main()

Inside main() function, how can I check if var parameter got True value by default, or it was passed by the user?

What I want to achieve: I will have few flags. When the user does not pass any of the flags, I want them all to be True. When the user passes at least one of the flags, only the passed flags should be True, the other flags False.

As I haven't really used click - maybe there's some functionality to handle this but as a workaround, I'd set the default value to None and check against if the value if its None when command is called. Something like this:

import click

@click.command
@click.option('-f/-F', 'var', default=None)
def main(var):
    if var is None:
       var = True
       print("No Value Provided - default to True")
    click.echo(var)

main()