def update_dict(src_dict: dict, tgt_dict: dict) -> dict:
    """
    Update tgt_dict with src_dict.
    * Notice that changes will happen only on keys which src_dict holds.

    Parameters
    ----------
    src_dict : dict
    tgt_dict : dict

    Returns
    -------
    tgt_dict : dict

    """

    for k, v in src_dict.items():
        tgt_v = tgt_dict.get(k)
        if tgt_v is None:
            tgt_dict[k] = v
        elif not isinstance(v, dict):
            tgt_dict[k] = v
        else:
            update_dict(v, tgt_v)
    return tgt_dict