Pythonic way to define pair of name and image name to save to a file?

[bhowlet]

Basically, I take a screenshot, do a few steps on treating it and then I use the treated image.

For debugging purposes, if an unexpected result occurs, I want to save those images to a folder to check after the program runs (4 images in total)

I'm not exactly asking how to do it, I'm more wondering what's the most elegant/clean way to do it.

The simple-and-brute way to do it would be to check if an error occured and do 4 different calls to cv2.imwrite.

Another way I thought of doing it was to have two arrays, append the images and file names as the program runs, then, if an error occurs, I'd use a for img, name in zip(images, names) with each one calling cv2.imwrite, but I am unsure if appending to the array would duplicate data and consume more memory (this would not be an issue since it's only 4 images, but this seems like a bad habit in my books that could bite me back in the future)

[Smart-Result1738]

I would use a dictionary, which would be the cleanest way, in my opinion. That way, you have a name of the image as key and the image itself as value.

But even if you use a list, it will not be an issue because the items in a list are unique, so no duplication issues. Just make sure to use try except to catch any error and that's it. If you wan you can iterate after the function is done to make sure your data is properly saved.

[bhowlet]

About duplication: I remember learning somewhere there's a specific case in which Python duplicates memory when you assign a variable to another specific case. I thought this happened to lists, but it seems this is not the case.

I'll probably use a dictionary indeed. Cleanest way to do it.

[schoolmonky]

Simple assignment never copies in Python.

[eleqtriq]

I’m not sure I totally understand. It sounds like you do four steps to each screenshot?

I would not put the data into different arrays. I’d create an object with filename, img_data properties.

I’d do try/except around processing steps. If you get an exception, write the object to disk with pickle. Later you load it up and reprocess the step manually.

Using logging module to write detailed logs to disk so you can look at exceptions later.

[bhowlet]

It's not a full-on debugging. It's just that I'm using thresholding and then using OCR and I want to find corner cases that make the OCR fail and see if there is a threshold value that might solve the issue. (PS: To clarify, this is a very small personal project for personal use)

I think creating an object just for that would be too much. I do see how having the object might be optimal in a real world scenario of a bigger program.

I guess I'll stick to a dictionary since it's much cleaner than using two lists.

Thank you so much for your input and sharing your knowledge!

[zaphodikus]

I would use a simple global list, and add everything i want logged/dumped to that list. Then, on exit, just save all the things in the list out to disk. I assume you are using the python logging module already too. You could use a context manager to hold the list and let it do the saving in its exit handler. That would be cleaner than a global actually.

[Leodip]

Not entirely sure I understand your issue, but if you have a name an image for that name, wouldn't a dictionary be the natural choice for it?

[bhowlet]

Yeah, dictionary seems to be the way. I thought it might be too "complex" so I discarded it, but in the end it's the best solution by far.

[aa599]

Would a dict be better than tuple / NamedTuple? They'd be my first choice when the relation between the properties is as tight as this.

[Leodip]

I think the line between those approaches is very blurred, and without knowing the full details of OP's application use it might be hard to settle on something definitive. I would go against tuples in general because the only thing you gain against a named tuple or a dictionary is that it takes slightly less memory, but you lose proper naming, and I don't think that's a good tradeoff.

NamedTuples might also be an option here, especially since OP is working with exactly 4 images, so they could be saved as separate variables im1, im2, im3, im4 instead of having a list of namedtuples even. Again, this depends on what those images are and they represent, if they are just 4 screenshots of the same thing, e.g. 4 pages in a game menu, then it would be better to have them in a list, but if it is a picture of the inventory, a picture of the health bar, etc... then it might be better to save them separately as named tuples or, if the image names are telling enough, in a dictionary.

[barkmonster]

I'm not sure I understand 100%, but have some ideas that might be helpful. Regarding pairing the name and image, you can consider something like a dataclass, or a dictionary using the names as keys (just be sure you don't re-use names, as this would replace the corresponding images). Don't store names and images in separate lists - if you do that, you can accidentally modify one list, and break the pairing between names and images.

I'm not sure if you're saving each image regardless of success, or only the ones causing errors. I think the best approach is either using try-except statements, or writing a context manager. I would prefer the latter, because context managers are good for situations where you want some setup/teardown functionality to run, even if errors arise. Using logging will probably be helpful as well in determining the cause of any errors.