Oleg Broytmann wrote:
On Fri, May 19, 2006 at 10:12:23AM -0500, Ian Bicking wrote:
It inherits __nonzero__ already (so SelectResults are always true), but
does not implement __len__. Like I said, I really dislike those very
few instances where you might encounter objects you can't test an object
for truth, so I'm not very positive about that resolution. But I don't
know, that's really the only way to keep people from introducing bugs
into their code, since it's so natural (but probably incorrect) to test
a SelectResult for truthfulness.
We have to choose among the following possibilities:
1) implement __nonzero__() via count() and warn users that it's slow;
2) completely forbid __nonzero__() by raising an exception;
3) allow users to choose; write some classes that a user use to choose the
desired behavior.
1) No one will see our warning, unless we actually make it a warning,
which is annoying and might as well be an exception IMHO.
2) Also annoying. You have to do more explicit tests then, like "is
None" to avoid triggering __nonzero__.
3) I hate choice, then no one knows what someone else's code is going to
be doing, help is harder to provide, etc.
I'm leaning toward 2, like:
def __nonzero__(self):
raise NotImplementedError(
"To test if a SelectResult will produce any items, use
list(result) or result.count()")
I'm not sure if it's a big backward compatibility problem, as I suspect
it will reveal as many bugs as it does correct code that won't work.
The only nuisance will be a place where people expect None, 0, and/or
other false items, and are using the current behavior to distinguish
those from SelectResult. That seems uncommon. If they just expect
None, replace it with "is None". If they expect None or empty
containers (like []), then treating SelectResult like a boolean is
probably an outstanding bug.
--
Ian Bicking / [EMAIL PROTECTED] / http://blog.ianbicking.org
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