def __all_have_key(fcs_objs, key):
    """Utility func to confirm all fcs objects have a specified parameter key.

    Args:
        fcs_objs: iterable of loaded FCSFile instances.
        key: str parameter key.

    Returns:
        bool: True if all fcs objs have key.
    """

    return all(fcs.has_param(key) for fcs in fcs_objs)