pygame.errror exceptions are too generic

[bendavis78]

• unit test for FileNotFoundError exception for pygame.image.load (good first issue)
• investigate where in the pygame code different exceptions could be raised (rwops.c? image_ext.c?)
• file opening code in src_c/ to raise FileNotFoundError when file isn't there.
• look at mapping other SDL file related error codes to python exceptions. Not just FiltNotFoundError.

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When loading an image with a file that doesn't exist, you get a pygame.error exception with a human-readable string description of the error. This is an anti-pattern. It would be better to allow the built-in exception IOError or FileNotFoundError to bubble up.

Let's say I want to handle an error where an image isn't found on disk. I currently have to check os.path.isfile(path). If the file does exist, and I use pygame.image.load(path), that's two file stats, which is not as efficient as simply catching the exception that is normally thrown when a file doesn't exist.

Either the original exception should be allowed to raise, or pygame should define its own version of FileNotFoundError. There may be other instances of this anti-pattern throughout pygame, but so far this is all I've come across.

[illume]

This is a good enhancement.

I don't have time to do this myself anytime soon, but PRs are welcome. The first step would be to make some unit tests. I've added a task list.

[krkakade]

Can I work on it?

[vjs22334]

I would like to work on this if it's still available

[MightyJosip]

Of course, any help would be appreciated

[jshultz]

I would be interested to work on this as well.

[illume]

Here are a couple of error codes that IMG_GetError returns.

>>> import pygame
pygame 2.0.0.dev7 (SDL 2.0.12, python 3.7.4)
Hello from the pygame community. https://www.pygame.org/contribute.html
>>> pygame.image.load("asdf.png")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
pygame.error: Couldn't open asdf.png
>>> pygame.image.load("/etc/passwd")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
pygame.error: Unsupported image format

[illume]

Closing thanks to the PR from @dotmars that was merged. Thanks!