[Python-ideas] except expression

[Andrew Barnert]

On Feb 13, 2014, at 11:04, Nathan Schneider <nathan at cmu.edu> wrote:

> On Thu, Feb 13, 2014 at 1:47 PM, spir <denis.spir at gmail.com> wrote:
>> On 02/13/2014 07:43 PM, Amber Yust wrote:
>>> Actually. What if we just reused 'try'?
>>> 
>>>      foo = bar() except BazException try 'qux'
>>> 
>>> This also leads naturally to chaining multiple possible fallbacks:
>>> 
>>>      foo = bar() except BarException try baz() except BazException try None
>> 
>> I like it. Especially because 'try' already works with 'except'. (But note that 'try', like my proposal of 'then', normally introduces a block).
> 
> This strikes me as counterintuitive because it is inconsistent: 'bar()' is being tried, but does not follow 'try', while the others do. And then the 'try None' has no corresponding 'except'.
> 
> Suggestion: an expression like
> 
>     foo = (try bar() except BarException)
> 
> that defaults to None if the exception is caught. This could then be chained with 'or':
> 
>     foo = (try bar() except BarException) or (try baz() except BazException)

But what if bar() can successfully return None, or just a falsey value in general?

Note that this is exactly the reason we needed the if expression: because or is tempting but incorrect in such cases.

> 
> as distinguished from
> 
>     foo = (try bar() except BarException) or baz()
> 
> which does not do any exception handling for baz().
> 
> (Apologies if something like this has been proposed above; I could not find it from skimming the thread.)
> 
> Nathan
>  
>> 
>> d
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