weakref, memory management and execution slow down in PyQt4

Michael Torrie torriem at gmail.com
Tue Sep 9 17:32:19 CEST 2014


Reposting to list, instead of directly to kjs

On 09/08/2014 08:45 PM, kjs wrote:
> Thanks for the consideration Michael. If you do get the data, and are
> able to run the code, let me know if you notice anything interesting.

Yeah I don't think I'll be able to have the time to download a 3 GB file.

>> Is there a reason you are using setattr and getattr instead of a proper
>> data structure?  both of those calls are rather expensive.  Would
>> probably be cheaper to use some kind of array, dictionary, or other
>> purpose-built data structure?
>>
>
> You're right, a dictionary can do everything I need and more. This
> happened to be the first thing I thought of, and I didn't imagine it
> would be very expensive. I figured it was simply a different way of
> defining and retrieving a class variable. IE setattr(self, foo, True) ==
> self.foo = True.

Yes you're correct.  It is the equivalent.  But it always involves
lookup in the object's dictionary, which is big O order O(n log n)
complexity for each and every access.  A list would be far faster,
essentially O(1) (I think?) after the single name lookup, since you can
access the elements by number.  Indexing into a list doesn't involve
doing name lookups; you just specify an offset.  No idea how much
faster, but significantly so.  If a list is too slow, there are other
array-like classes you can use (like numpy arrays) that do offer true
O(1) lookups.

Besides that, it's not typical use of setattr and getattr in python.





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