But having exceptions without '__traceback__' affects not
only the inspect module, but also lots of other code. It
will make harder to write generic error reporting code, as
you'd need to check for __traceback__ first, and then, if
it's None, look for some other, asyncio specific attribute.
I think that having tracebacks with fake frames is much
more backwards compatible and consistent solution. I don't
understand why we should break the established protocol
here.
[Or we can allow instantiation of immutable frame objects
without __code__]
Yury
On 2014-03-06, 1:32 PM, Guido van Rossum wrote:
But inspect is in the stdlib. Surely changing inspect.py is less
controversial than amending the semantics of frame objects.
On Thu, Mar 6, 2014 at 10:10 AM, Xavier Morel <python-...@masklinn.net>wrote:
On 2014-03-06, at 16:52 , Antoine Pitrou <solip...@pitrou.net> wrote:
Le 06/03/2014 16:03, Yury Selivanov a écrit :
On 2014-03-06, 8:42 AM, Antoine Pitrou wrote:
Le 05/03/2014 23:53, Nick Coghlan a écrit :
__traceback__ wouldn't change [...]
Uh, really? If you want to suppress all reference cycles, you *have*
to remove __traceback__.
The problem is to make computation of the traceback summary
lightweight enough that it doesn't degrade performance in the common
case where you don't have to print the traceback later.
So why can't we allow instantiation of types.TracebackType &
types.FrameType?
IMO it is absolutely out of question to allow creation of arbitrary
frames from Python code, because the structure and initialization of frames
embody too many low-level implementation details.
We might allow the creation of traceback objects, but without any custom
frame objects it is unclear how useful that would be.
Some bits of the standard library (and probably third-party libraries
transitively relying on getinnerframes) really, really want traceback
objects and can't be used with a stack or frames extracted via
inspect.currentframe() or whatever. For instance cgitb.text calls
inspect.getinnerframes which accesses param.tb_frame then calls
getframeinfo(param). getframeinfo blows up if it does not get either an
actual traceback object or an actual frame object.
A frame object does not have a tb_frame attribute, and will thus fail
in getinnerframes, a fake traceback object will fail in getframeinfo.
Therefore it's not possible to call cgitb.text outside of an exception
handling context (that is, not possible to use it as a
traceback.print_stack providing extra information). If it were possible
to create traceback objects, there would be no issue there at least.
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