Why is a Bare `except` Statement in Python Risky, and How Can You Handle Exceptions More Safely?

What are the Pitfalls of an Unqualified 'except' in Python?

In your quest to determine the presence of an image on the screen using PyAutoGUI, you devised a function that triggered a warning from PyCharm. The source of this warning lies in the bare 'except' statement.

The Issue with a Bare 'except'

An unqualified 'except' serves as a catch-all for all exceptions, including those that you likely don't intend to handle. This can include critical exceptions such as KeyboardInterrupt, SystemExit, and other Python-raised errors.

Recommended Approach

To mitigate these potential issues, it's advisable to specify the types of exceptions you anticipate encountering. In your case, PyAutoGUI defines an ImageNotFoundException specifically for situations where the image is absent. By using:

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

you refine your exception handling to target the expected failure state.

Principles of Exception Handling

It's crucial to note that exception blocks should be reserved for handling known and recoverable failure scenarios. If an unknown or irrecoverable error occurs, it's preferable to allow it to propagate up the call stack. In such cases, the default behavior of the Python interpreter is to terminate with an uncaught exception.

By selectively catching specific exceptions, you ensure that your function can recover gracefully from expected errors, while allowing more severe issues to trigger the appropriate response.

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