I think this boils it down to the essence. Whether you use a trailing comma here, and whether you use single or double quotes, is just bike-shedding. If there's an automated tool that can make a consistent choice everywhere, that's worthwhile.

I don't see "pietnas" anywhere; do you mean the "important_numbers" example from maratc?

If so, I think a trailing comma is the correct fix, as described here: https://news.ycombinator.com/item?id=45168308

In this case I think the trailing comma is an improvement, so the formatter is steering you towards a better overall solution. However, even if you dislike the trailing comma, it's more important for the formatting to be consistent and robust, so I still think it's better to work within the limitations of the formatter.

It can’t be just that, surely? Or the more traditional sloped fronts would be gone completely.

I don’t think people are buying these because they’re safer for pedestrians, they’re buying them because they like the way they look, and/or because they (the drivers) feel safer when they’re in a huge box sitting high up, looming over the surrounding cars.

It works the way you want if you add a trailing comma:

  important_numbers = {
    "x": 3,
    "y": 42,  # Answer to the Ultimate Question!
    "z": 2,
  }

The trailing comma is an improvement as it makes the diff clearer on future edits.

Edit to add: occurs to me that I oversimplified my position earlier and it probably looks like I'm trying to have it both ways. I do advocate aiming for clean and clear formatting; I'm just against doing this manually. You should instead use automation, and steer it lightly only when you have to.

For example, I explicitly don't want people to manually "tab-align" columns in their code. It looks nice, sure, but it'll inevitably get messed up in future edits. Better to do something simpler and more robust.

I don't think we'll ever fully agree, but I'd just like to clarify that I value that kind of craftsmanship too!

I just honestly believe that if you fully automate the formatting, the results are better than if you do it painstakingly by hand; better by virtue of being more consistent. It's using the right tool for the job.