On 2/1/2012 3:07 PM, Guido van Rossum wrote:
On Wed, Feb 1, 2012 at 10:48 AM, Ethan Furman<et...@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
_______________________________________________
Python-Dev mailing list
Python-Dev@python.org
http://mail.python.org/mailman/listinfo/python-dev
Unsubscribe:
http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
