def update_if(cur_dict, ap_dict):
    """Adds item to the dict if key is not already in dict

    Parameters
    ----------
    cur_dict : dict
        The dictionary we wish to update

    ap_dict : dict
        The dictionary we want to append to the current dictionary
        without overwriting any current keys

    Returns
    -------
    cur_dict : dict
        The dictionary that has been updated
    """
    assert type(cur_dict) == type(ap_dict) == dict
    "type must be a dict"
    for key in ap_dict:
        if key not in cur_dict:
            cur_dict[key] = ap_dict[key]
    return cur_dict