@Nullable
  private static PyExpression toExpression(@NotNull String contents, @NotNull PsiElement anchor) {
    final PsiFile file = FileContextUtil.getContextFile(anchor);
    if (file == null) return null;
    PyExpression fragment = PyUtil.createExpressionFromFragment(contents, file);
    if (fragment != null) {
      fragment.getContainingFile().putUserData(FRAGMENT_OWNER, anchor);
    }
    return fragment;
  }
@Nullable
  private static PyExpression toExpression(@NotNull String contents, @NotNull PsiElement anchor)