def METHOD_NAME(etype2files, symmetry):
    if symmetry:
        etype_list = []
        for etype in etype2files.keys():
            r_etype = get_inverse_etype(etype)
            etype_list.append(etype)
            if r_etype != etype:
                etype_list.append(r_etype)
    else:
        etype_list = list(etype2files.keys())
    return etype_list