From: Arlen Cuss <celtic@...>
Date: 2008-04-01T15:51:37+09:00
Subject: Re: begin/rescue not behaving how I want

------=_Part_11491_9895103.1207032695293
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Content-Disposition: inline

Check out these two cases:

celtic@sohma:~$ irb
>> begin
?> raise TimeoutError, "data"
>> rescue
>> puts "Test?"
>> end
(irb):2:in `irb_binding': data (Timeout::Error)
    from /usr/lib/ruby/1.8/irb/workspace.rb:52:in `irb_binding'
    from /usr/lib/ruby/1.8/irb/workspace.rb:52

celtic@sohma:~$ irb
>> begin
?> raise TimeoutError, "data"
>> rescue TimeoutError => t
>> puts "Error with #{t}."
>> end
Error with data.
=> nil
>>

In the first one, the exception is raised (and irb doesn't catch it and
dies). In the second one, we explicitly catch TimeoutError, and it's fine.
Why so?

TimeoutError isn't a "StandardError", which is the default thing that
`rescue' tries to rescue when you leave it blank!

>> TimeoutError.superclass
=> Interrupt
>> Interrupt.superclass
=> SignalException
>> SignalException.superclass
=> Exception
>>

Notice that it goes TimeoutError < Interrupt < SignalException < Exception.
Whereas, for example...

>> ZeroDivisionError.superclass
=> StandardError
>> StandardError.superclass
=> Exception
>>

A ZeroDivisionError is of superclass StandardError (which is then an
Exception). So it would get caught.

To catch all cases, try rescue Exception -- or REALLY all cases with rescue
Object. (if you're crazy.) But of course, try not to catch anything you're
not expecting - that's how unexpected errors turn up. Instead, perhaps just
rescue Timeout (if it's the only error you expect). That way other errors
you don't expect aren't silently thrown away [leading to frustration for you
when you try to debug!]

Cheers,
Arlen.
On Tue, Apr 1, 2008 at 3:49 PM, J. Cooper <nefigah@gmail.com> wrote:

> So I have some code that routinely checks for email in a cron job. Most
> of the time it works great. However, sometimes it gets a timeout error,
> which is fine; it happens. The thing is, I don't want it to clog up my
> logs when it does, because it's not an exception I'm worried about. So I
> tried wrapping the code in question in a begin/rescue block that just
> exits on exception, thinking that then it the error would be "caught"
> and it wouldn't have to bug me about it... but it continues to do so.
> How do I get what I want to achieve here?
>
> (The relevant code, if needed):
> begin
>  Net::POP3.start('foo', 110, 'bar', 'foobar') do |pop|
>   if pop.mails.empty?
>     exit
>   else
>     # blah blah etc.
>   end
>  end
> rescue
>  exit
> end
> --
> Posted via http://www.ruby-forum.com/.
>
>

------=_Part_11491_9895103.1207032695293--