Returns a better error message when invalid configuration option
    is provided.

def invalid_config_error_message(action, key, val):
    """Returns a better error message when invalid configuration option
    is provided."""
    if action in ('store_true', 'store_false'):
        return ("{0} is not a valid value for {1} option, "
                "please specify a boolean value like yes/no, "
                "true/false or 1/0 instead.").format(val, key)

    return ("{0} is not a valid value for {1} option, "
            "please specify a numerical value like 1/0 "
            "instead.").format(val, key)