How to add attachment to cell from Python formula?

Hello! I’d like to download image from parsed web page and add it to Grist cell. I would do it from the cell itself (from Trigger formula). No problem to add any kind of parsed text this way but I can’t understand how to add image to a cell?

And one more question: running Python formulas in Grist multi-threaded or not? I mean, all cells calculated parallel, or not?

And one more question: is it possible to alter other cells in a current row from the formula? Because I run URL request I don’t want to run it again in each cell, just want to populate different cells from a single call. On the other hand, I don’t want to over-complicate it making external interactions and prefer to program it right in the Grist.

I do it on a self-hosted installation with additional Python modules installed.