[Python-Dev] PEP for allowing 'raise NewException from None' (original) (raw)

Guido van Rossum guido at python.org
Fri Jan 27 20:54:31 CET 2012

On Fri, Jan 27, 2012 at 9:08 AM, Ethan Furman <ethan at 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. It seems to me that generating the amount of information needed to track down errors is a balancing act between too much and too little; forcing the print of previous context when switching from exception A to exception B feels like too much:  at the very least it's extra noise; at the worst it can be confusing to the actual problem.  When the library (or custom class) author is catching A, saying "Yes, expected, now let's raise B instead", A is no longer necessary. Also, the programmer is free to not use 'from None', leaving the complete traceback in place.

Ok, got it. The developer has to explicitly say "raise from None" and that indicates they have really thought about the issue of suppressing too much information and they are okay with it. I dig that.

-- --Guido van Rossum (python.org/~guido)

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