Python 'except' fall-through

Question

I was wondering if you could re-raise a (specific) caught exception and have it caught by a later (general) except in the same try-except. As an example, I want to do something with a specific IOError, but if its not the expected IOError then the exception should be handled like any other error. What I initially tried:

try:
    raise IOError()
except IOError as ioerr:
    if ioerr.errno == errno.ENOENT:
        # do something with the expected err
    else:
        # continue with the try-except - should be handled like any other error
        raise
except Exception as ex:
    # general error handling code

However, this doesn't work: the raise re-raises the exception outside the context of the try-except. What would be the pythonic way of writing this to get the desired exception 'fall-through' behaviour?

(I'm aware there was a proposed 'conditional except' that wasn't implemented, which could've solved this)

Answer 1

If you ultimately want it to catch everything, make it do that. Catch first, sieve later. ;)

try:
    raise IOError()
except Exception as ex:
    if isinstance(ex, IOError) and ex.errno == errno.ENOENT:
        # do something with the expected err
    # do the rest

Answer 2

I am not an expert in writing pythonically, but I think one obvious approach (if you know that you're expecting one particular kind of exception), would be to use nested exception handling:

try:
    try:
        raise IOError()
    except IOError as ioerr:
        if ioerr.errno == errno.ENOENT:
            # do something with the expected err
        else:
            # pass this on to higher up exception handling
            raise

except Exception as ex:
    # general error handling code

I know in your comment that you didn't want nested else's -- I don't know if nested exception handling is as bad in your book, but at the very least you can avoid code duplication.