def METHOD_NAME(username=None, acronym=None):
    assert username or acronym
    if acronym:
        group = get_object_or_404(Group, acronym=acronym)
        clist = CommunityList.objects.filter(group=group).first() or CommunityList(group=group)
    else:
        user = get_object_or_404(User, username__iexact=username)
        clist = CommunityList.objects.filter(user=user).first() or CommunityList(user=user)
    return clist