Catch only some runtime errors in Python

Question

I'm importing a module which raises the following error in some conditions: RuntimeError: pyparted requires root access

I know that I can just check for root access before the import, but I'd like to know how to catch this spesific kind of error via a try/except statement for future reference. Is there any way to differentiate between this RuntimeError and others that might be raised?

Answer 1

You can check attributes of the exception to differentiate from other possible RuntimeError exceptions. For example, re-raise the error if it does not match a predefined message text.

    try:
        import pypatred
    except RuntimeError,e:
        if e.message == 'RuntimeError: pyparted requires root access':
            return 'pyparted - no root access'
        raise

Of course, direct text comparison is just an example, you could search for included substrings or regular expressions.

It is worth noting that the .message attribute of exceptions is deprecated starting with Python 2.6. You can find the text in .args, usually args[0].

... For 2.6, the message attribute is being deprecated in favor of the args attribute.

Answer 2

I know that I can just check for root access before the import, but I'd like to know how to catch this spesific kind of error via a try/except statement for future reference. Is there any way to differentiate between this RuntimeError and others that might be raised?

If the error is caused by a specific condition, then I think the easiest way to catch the error is to test for the condition, and you can raise a more specific error yourself. After all the 'error' exists before the error is thrown, since in this case its a problem with the environment.

I agree with those above - text matching on an error is kind of a terrifying prospect.

Answer 3

try:
    import pyparted
except RuntimeError:
    print('RuntimeError is raised')
    raise

more on exception handling in tutorial.

This situation should produce ImportError in my opinion. And you can do it yourself:

try:
    import pyparted
except RuntimeError as e:
    raise ImportError(e)