Ethan Furman wrote:
Steven D'Aprano wrote:
On Fri, 02 Apr 2010 19:48:59 -0700, Ethan Furman wrote:
The heuristic I use is, if I expect the try block to raise an exception
more than about one time in ten, I change to an explicit test. In this
case, since the exception should only be raised once, and then never
again, I would use a try...except block.
That was my reasoning as well, but when I timed it for one million runs
(so 1 instantiation, 999,999 simple calls), the __getattr__ time was .5
seconds, the try...execpt block was .6; at ten million it was 5 and 6.
Care to share your timing code? Not that I don't trust your results,
but timings are very sensitive to the exact thing you do, and I'd like
to see what that is.
Happy to do so -- if I made a mistake I'd like to know about it and learn.
It'll have to wait two days 'til I get back to work, though... I'll post
it asap.
Well, so much for asap, but here's what I used (with one correction: in
the 'if' code I had forgotten to actually reference the missing
attribute, so the __getattr__ look up never happened; now the
try...except block is /slightly/ faster, as opposed to 20% slower).
class spam_except(object):
def __call__(self, x, y, z):
try:
mongo = self.mongo
except AttributeError:
mongo = self.mongo = 1
return
class spam_if(object):
def __getattr__(self, name):
if name != 'mongo':
raise AttributeError
self.mongo = 1
return self.mongo
def __call__(self, x, y, z):
self.mongo # didn't have this line before. d'oh!
return
--> timeit.Timer('spammer(1,2,3)','from spam import spam_except;
spammer=spam_except()').timeit()
0.65764130543749388
--> timeit.Timer('spammer(1,2,3)','from spam import spam_if;
spammer=spam_if()').timeit()
0.66972877235545525
~Ethan~
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