Clean way to return error codes

[Peter Otten]

Steven D'Aprano wrote:

> I have a script that can be broken up into four subtasks. If any of those
> subtasks fail, I wish to exit with a different exit code and error.
> 
> Assume that the script is going to be run by system administrators who
> know no Python and are terrified of tracebacks, and that I'm logging the
> full traceback elsewhere (not shown).
> 
> I have something like this:
> 
> 
> try:
>     begin()
> except BeginError:
>     print("error in begin")
>     sys.exit(3)
> 
> try:
>     cur = get_cur()
> except FooError:
>     print("failed to get cur")
>     sys.exit(17)
> 
> try:
>     result = process(cur)
>     print(result)
> except FooError, BarError:
>     print("error in processing")
>     sys.exit(12)
> 
> try:
>     cleanup()
> except BazError:
>     print("cleanup failed")
>     sys.exit(8)
> 
> 
> 
> It's not awful, but I don't really like the look of all those try...except
> blocks. Is there something cleaner I can do, or do I just have to suck it
> up?

def run():
    yield BeginError, "error in begin", 3
    begin()

    yield FooError, "failed to get cur", 17
    cur = get_cur()

    yield (FooError, BarError), "error in processing", 12
    result = process(cur)
    print(result)

    yield BazError, "cleanup failed", 8
    cleanup()

try:
    for Errors, message, exitcode in run():
        pass
except Errors:
    print(message)
    sys.exit(exitcode)