[Python-ideas] (no subject)

[Yury Selivanov]

I actually thought about adding 'Exception.__hint__' attribute which 
would have a longer message explaining what happened and how to fix it.  
displayhooks can be easily modified to print __hint__ when it's set.  We 
can then add C API to set hints.


To address any possible performance concerns, we can disable hints in -O 
mode (essentially we can make them almost zero-cost).


Yury

On 2016-11-29 12:43 PM, Brett Cannon wrote:
> On Tue, 29 Nov 2016 at 02:39 Nathaniel Smith <njs at pobox.com> wrote:
>
>> On Tue, Nov 29, 2016 at 1:05 AM, Victor Stinner
>> <victor.stinner at gmail.com> wrote:
>>> Hi,
>>>
>>> Python is optimized for performance. Formatting an error message has a
>>> cost on performances.
>> Sure, but we have to look at this on a case-by-case basis. Is there
>> really important code out there that's generating NameErrors or
>> SyntaxErrors in an inner loop? That seems unlikely to me.
>>
>> Even IndexError I'm a bit skeptical about. I can believe that there's
>> code that intentionally generates and then catches IndexError, but
>> AttributeError in my experience is much more performance-sensitive
>> than IndexError, because every failed hasattr call allocates an
>> AttributeError and hasattr is commonly used for feature checks. Yet
>> AttributeError has a much more informative (= expensive) message than
>> IndexError:
>>
>> In [1]: object().a
>> AttributeError: 'object' object has no attribute 'a'
>>
>> In [2]: list()[0]
>> IndexError: list index out of range
>>
> One way to make this cheap is to have a reasonable default message and use
> attributes on the exceptions trigger the use of the default message. Nearly
> a year ago I filed a bunch of issues for ideas on providing attributes on
> exceptions where it made sense, e.g. an index attribute on IndexError (
> http://bugs.python.org/issue18162). If we did this then for classes like
> IndexError there constructor could be `IndexError(index=10, start=0,
> end=3)` and then __str__() can lazily construct the string representation
> using a default message, e.g. `"index {} is out of range of{} to
> {}".format(index, start, end)`. Make the arguments keyword-only and they
> become backwards-compatible and so the only overhead you pay for these
> richer messages are keyword-based construction if you simply never access
> the repr for the exception.
>
>
>
> _______________________________________________
> Python-ideas mailing list
> Python-ideas at python.org
> https://mail.python.org/mailman/listinfo/python-ideas
> Code of Conduct: http://python.org/psf/codeofconduct/