@Nullable
  public static PsiDirectory stepBackFrom(PsiFile base, int depth) {
    if (depth == 0) {
      return base.getContainingDirectory();
    }
    PsiDirectory result;
    if (base != null) {
      base = base.getOriginalFile(); // just to make sure
      result = base.getContainingDirectory();
      int count = 1;
      while (result != null && PyUtil.isPackage(result, base)) {
        if (count >= depth) return result;
        result = result.getParentDirectory();
        count += 1;
      }
    }
    return null;
  }
@Nullable
  public static PsiDirectory stepBackFrom(PsiFile base, int depth)