[Python-Dev] PEP 409 and the stdlib

[Hrvoje Niksic]

On 05/21/2013 02:57 PM, Serhiy Storchaka wrote:
> 21.05.13 13:05, Hrvoje Niksic написав(ла):
>> On 05/21/2013 11:56 AM, Serhiy Storchaka wrote:
>>> try:
>>>       x = d['key']
>>> except KeyError:
>>>       x = fallback('key')
>>>
>>> def fallback(key):
>>>       if key not in a:
>>>           raise BusinessError(...)
>>>       return 1 / a[key] # possible TypeError, ZeroDivisionError, etc
>>
>> Yes, in that case the exception will appear unintentional and you get
>> the old message — it's on a best-effort basis.
>
> In both cases the BusinessError exception raised explicitly. How do you
> distinguish one case from another?

In my example code the "raise" keyword appears lexically inside the 
"except" clause.  The compiler would automatically emit a different 
raise opcode in that case.

NB in your example the "raise" is just as intentional, but invoked from 
a different function, which causes the above criterion to result in a 
false negative.  Even in so, the behavior would be no worse than now, 
you'd just get the old message.

Hrvoje