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. _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
