Try/except vs. if/else

Stephen Horne $$$$$$$$$$$$$$$$$ at $$$$$$$$$$$$$$$$$$$$.co.uk
Mon Sep 29 20:08:23 CEST 2003


On Mon, 29 Sep 2003 10:33:27 +0100, Tim Rowe
<tim at remove_if_not_spam.digitig.co.uk> wrote:

>Internal constructs don't bother me -- ultimately it all comes down to
>machine code which will be a mass of goto's.  That doesn't mean that
>my code should be (could be!) a mass of goto's.
>
>And the last time I needed a goto for anything I was programming in
>BASIC; I don't need to use exceptions to emulate it in a language with
>decent flow control constructs (Python qualifies, of course!).

Ah - a good old goto debate ;-)

I have long claimed that goto is useful in rare circumstances, that it
can be clearer and more maintainable than structured code in those
rare cases, and that while anything can be abused it is still
perfectly possible for a good programmer to use it responsibly and to
refactor when the code becomes too messy. Structured, OO, and indeed
any style of programming can become unreadable and unmaintainable
(hence the fuss about refactoring).

That said, it was quite a shock when I actually found a case where I
needed a goto about six months ago. Quite literally I made several
attempts at writing a function in a structured way and got it wrong
each time. Each time I came back to it the previous version seemed a
horrible mess so I rewrote it. Eventually I figured this was stupid,
especially as it didn't seem so hard in my head. I put that mental
picture onto paper - and as I did so I realised it simply wasn't a
structured job. It was very much a state transition model. But because
it completes all its work in one go, and doesn't need to maintain the
state between calls, it simply hadn't occurred to me to think of it
that way.

I remember telling a college lecturer that if state transition models
are appropriate for some things then so must gotos be appropriate, and
that in a 'short running' state machine a goto would be the logical
way to implement the transitions. At the time, I didn't think it would
be so long before I found an example ;-)

Anyway, this example was in some fairly low level library code I was
writing in C++. I don't see any need for goto in Python, trust that it
will never be added, and don't like to see exceptions abused that way.

Just sharing a rather pointless anecdote.


-- 
Steve Horne

steve at ninereeds dot fsnet dot co dot uk




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