[Python-Dev] PEP 463: Exception-catching expressions

Ethan Furman ethan at stoneleaf.us
Sat Feb 22 01:42:36 CET 2014

On 02/21/2014 11:04 AM, Yury Selivanov wrote:
> On 2/20/2014, 10:15 PM, Chris Angelico wrote:
>> * list.pop() - no way to return a default
> We can fix that in 3.5.

How many are you going to "fix"?  How are you going to "fix" the routines you don't control?

>> * seq[index] - no way to handle a bounds error
> We can add 'list.get(index, default)' method, similar to
> 'Mapping.get'. It's far more easier than introducing new
> syntax.

When I have to keep writing the same code over and over and aver again, I find a better way to do the job.  In this 
case, an exception expression does quite nicely.

> I also searched how many 'except IndexError' are in
> the standard library code.  Around 60.  That's a rather
> low number, that can justify adding 'list.get' but not
> advocate a new syntax.

And roughly 200 of KeyError, another couple hundred of ValueError...

This is not just about better handling of [missing] default values, but of better exception handling.  This PEP adds the 
ability to use a scalpel instead of a sledge hammer.


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