Nick Coghlan wrote:
On Sat, Jan 28, 2012 at 10:33 AM, Ethan Furman <et...@stoneleaf.us> wrote:
So the question is:
- should 'raise ... from ...' be legal outside a try block?
- should 'raise ... from None' be legal outside a try block?
Given that it would be quite a bit of work to make it illegal, my
preference is to leave it alone.
I believe that means there's only one open question. Should "raise ex
from None" be syntactic sugar for:
1. clearing the current thread's exception state (as I believe Ethan's
patch currently does), thus meaning that __context__ and __cause__
both end up being None
2. setting __cause__ to None (so that __context__ still gets set
normally, as it is now when __cause__ is set to a specific exception),
and having __cause__ default to a *new* sentinel object that indicates
"use __context__"
I've already stated my own preference in favour of 2 - that approach
means developers that think about it can explicitly change exception
types such that the context isn't displayed by default, but
application and framework developers remain free to insert their own
exception handlers that *always* report the full exception stack.
The reasoning behind choice two makes a lot of sense. My latest effort
(I should be able to get the patch posted within two days) involves
creating a new dummy exception, SuppressContext, and 'raise ... from
None' sets cause to it; the printing logic checks to see if cause is
SuppressContext, and if so, prints neither context nor cause.
Not exactly how Nick describes it, but as far as I've gotten in my
Python core hacking skills. ;)
~Ethan~
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