def bool_formatter(bool_value):
    """
    convert Python boolean to json/xml format of boolean

    Parameters
    ----------
    bool_value: bool
        the boolean value that needs to be converted

    Returns
    -------
    str
        either "true" or "false"

    """
    if isinstance(bool_value, bool):
        if bool_value:
            return("true")
        else:
            return("false")
    else:
        msg = "bool_value must be a boolean"
        raise ValueError(msg)