[Q] Are Exceptions used that much in practice?

[Greg Ewing]

Jerome Mrozak wrote:
> 
> An example of compulsion is java.lang.Integer.parseInt(), which throws a
> NumberFormatException you *must* deal with or the program won't
> compile.

Ah, I see what you mean. No, there's never a case where you 
really *have* to catch an exception. You always have the 
option of ignoring exceptions; an exception which isn't 
caught anywhere will simply cause the program to abort 
with a traceback.

Sometimes you will want to catch exceptions, but those cases
are very rare, in my experience. Most of the time you can
write code without thinking about exceptions at all.

> I'm aware of examples of Python such as (faking it here):
> 
> while 1:
>   try:
>     input = inputFileObject.readline()
>   catch EOF:
>     break
>   else:
>     process(input)

Python doesn't report end-of-file by means of an exception;
it returns an empty string.

It does report I/O errors such as failing to open a file
with an exception, which is one of the few cases that you
will probably want to catch. You don't necessarily have
to put a try-except around every file open, though, and
that's probably not the best thing to do. A single
try-except somewhere high up in your program's logic
to catch any failures and report them to the user is
usually sufficient.

Hope that helps,

-- 
Greg Ewing, Computer Science Dept, University of Canterbury,	  
Christchurch, New Zealand
To get my email address, please visit my web page:	  
http://www.cosc.canterbury.ac.nz/~greg