[Python-Dev] PEP 409 - final? (original) (raw)

Terry Reedy tjreedy at udel.edu
Wed Feb 1 21:53:06 CET 2012

On 2/1/2012 3:07 PM, Guido van Rossum wrote:

On Wed, Feb 1, 2012 at 10:48 AM, Ethan Furman<ethan at stoneleaf.us> wrote:

Guido van Rossum wrote:

Hm... Reading this draft, I like the idea of using "raise X from None", but I still have one quibble. It seems the from clause sets cause, and cause can indicate three things: (1) print cause (explicitly set), (2) print context (default), (3) print neither (raise X from None). For (1), cause must of course be a traceback object. Actually, for (1) cause is an exception object, not a traceback. Ah, sorry. I'm not as detail-oriented as I was. :-) The PEP currently proposes to use two special values: False for (2), None for (3). To me, this has a pretty strong code smell, and I don't want this pattern to be enshrined in a PEP as an example for all to follow. (And I also don't like "do as I say, don't do as I do." :-) My apologies for my ignorance, but is the code smell because both False and None evaluate to bool(False)? That's part of it, but the other part is that the type of context is now truly dynamic. I often think of variables as having some static type, e.g. "integer" or "Foo instance", and for most Foo instances I consider None an acceptable value (since that's how pointer types work in most static languages). But the type of context you're proposing is now a union of exception and bool, except that the bool can only be False.

It sounds like you are asking for a special class NoException(BaseException) to use as the marker.

-- Terry Jan Reedy

More information about the Python-Dev mailing list