exception_example.py

class InvalidEmailAddressError(Exception):
    pass


def validate_email_address(ctx, param, value):
    regex = "^[a-z0-9]+[\._]?[a-z0-9]+[@]\w+[.]\w{2,3}$"
    if not re.search(regex, value):
        raise InvalidEmailAddressError(f"Invalid email address: {value}")
    return value


@click.command()
@click.option("--email", callback=validate_email_address)
def main(email):
    print(f"login: {email}")


if __name__ == "__main__":
    main()