Terry Reedy wrote:
On 1/27/2012 2:54 PM, Guido van Rossum wrote:
On Fri, Jan 27, 2012 at 9:08 AM, Ethan Furman<et...@stoneleaf.us> wrote:
Guido van Rossum wrote:
Did you consider to just change the
words so users can ignore it more easily?
Yes, that has also been discussed.
Speaking for myself, it would be only slightly better.
Speaking for everyone that wants context suppression (using Steven
D'Aprano's words): chained exceptions expose details to the caller
that are
irrelevant implementation details.
Especially if the users are non-programmer app users.
Or beginner programmers, e.g. on the python-list and tutor mailing lists. It
is hard enough to get beginners to post the entire traceback without making
them bigger. The typical newbie posts just the error message, sometimes not
even the exception type. What they will make of chained exceptions, I hate to
think.
I find double tracebacks to be 'jarring'. If there is a double bug, one
in both the try and except blocks, it *should* stand out. If there is
just one bug and the developer merely wants to rename it and change the
message, it should not.
Agreed with all of this.
[...]
The PEP does not address the issue of whether the new variation of raise
is valid outside of an except block. My memory is that it was not to be
and I think it should not be. One advantage of the 'as' form is that it
is clear that raising the default as something else is invalid if there
is no default.
I think that raise ... from None should be illegal outside an except block. My
reasoning is:
1) It ensures that raise from None only occurs when the developer can see
the old exception right there, and not "just in case".
2) I can't think of any use-cases for raise from None outside of an
except block.
3) When in doubt, start with something more restrictive, because it is
easier to loosen the restriction later if it turns out to be too much,
than to change our mind and add the restriction afterwards.
--
Steven
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