What is wrong with using a bare 'except'?

python except
CaioRamaglio picture CaioRamaglio · Mar 1, 2019 · Viewed 37.8k times · Source

I tried making a function to check if an image is displayed on the screen using PyAutoGui and came up with this:

def check_image_on_screen(image):
    try:
        pyautogui.locateCenterOnScreen(image)
        return True
    except:
        return False

And it works fine, but PyCharm tells me I shouldn't leave except bare. What is the problem with leaving it like this? Is there a more appropriate way of creating the same function?

Answer

Adam Smith picture Adam Smith · Mar 1, 2019

Bare except will catch exceptions you almost certainly don't want to catch, including KeyboardInterrupt (the user hitting Ctrl+C) and Python-raised errors like SystemExit

If you don't have a specific exception you're expecting, at least except Exception, which is the base type for all "Regular" exceptions.

That being said: you use except blocks to recover from known failure states. An unknown failure state is usually irrecoverable, and it is proper behavior to fatally exit in those states, which is what the Python interpreter does naturally with an uncaught exception.

Catch everything you know how to handle, and let the rest propagate up the call stack to see if something else can handle it. In this case the error you're expecting (per the docs) is pyautogui.ImageNotFoundException

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