As usual, Python has nice batteries included...
https://docs.python.org/3/library/tempfile.html#tempfile.NamedTemporaryFile

@halloleooo yes, sorry, my first (deleted and purged) answer was using format but only valid with pil

@halloleooo said:

there is a way via the UI builder

I don't think so but I never use the designer, thus perhaps it is better to have another advice

Just as a final follow-up: Using appex.get_attachments and Image.named works perfectly. Here my workflow:

I get the image file names via appex.get_attachments. I weed out the paths for heic files which have a accompaning other image file. Finally I load the remaining images manually via the Image.named method.

Thanks for your help, @cvp! :-)

Thanks @cvp. Works a treat! That's exactly what I want.

I wasn't aware of will_close but, of course, I found it now in the doco.

@halloleooo said:

Where do you know all these tricks from?

I'm sure this comes from the forum, full of amazing guys. This forum does not offer an easy way to search but if you use Google with "Pythonista forum pil ui.image" you should find it.

Of course, I have a lot of scripts thus I search among mines first.

Édit: I'm sure that if you use a lot Pythonista, you'll become one of these amazing guys 😀

@cvp Yes I did. Thx.

@cvp, sorry, I did not actually try it -- per the release notes there is supposed to be appex.get_ui.image().

didn't actually look -- but

@ccc I will post something in a few days when I clean some things up. I created an endless loop calling a function that wrote a large amount of data to a BytesIO. No crash. I downloaded objgraph, and this never showed any increase in BytesIO objects.

My attempt at writing an image viewer that uses pil2ui failed after 4 photos (with or without del bIO) because of apparently a bad image in my photos (at least one that PIL choked on). I will say that, in the case of displaying photos assets, one should be using .get_ui_image instead of .get_image. That avoids any round trip through PIL, which is probably where any leaks or bugs occur. A simple image viewer using get_ui_image ran for longer than I cared to wait without a crash.

Creating ui.Images also requires some care, because these might not get gc'd automatically. I believe the best practice is to include a with objc_util.autoreleasepool(): when many UIImages are created -- though I haven't had time to explore whether setting the imageview image causes the old image to get leaked (in which case it would be necessary to manually handle the deallocation of the UIImage object)

@cvp That's so super-cool! That's the perfect solution for me: Then I don't need global variables!

Thanks @ccc! I thought so, but good to be sure.

@mikael Good to know. Thanks!

@halloleooo i would not do that but I would call a function containing only the dialog and only the function would be decorated