C-style static variables in Python?

[Ethan Furman]

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~