def dict_flatten(dict_in: dict) ->dict:
    """Converts two levels dict to single level dict. Example input and output see _test_dict_flatten.
    :param dict_in: Any two levels (or less) dict.
    :return dict_out: Single level dict.
    """
    dict_out = dict()
    for k in list(dict_in.keys()):
        if isinstance(dict_in[k], dict):
            for kk, vv in dict_in[k].items():
                dict_out[f'{k}:{kk}'] = vv
        else:
            dict_out[k] = dict_in[k]
    return dict_out
