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 <n...@pobox.com> wrote:
On Tue, Nov 29, 2016 at 1:05 AM, Victor Stinner
<victor.stin...@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@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
_______________________________________________
Python-ideas mailing list
Python-ideas@python.org
https://mail.python.org/mailman/listinfo/python-ideas
Code of Conduct: http://python.org/psf/codeofconduct/
