Stefan Behnel, 30.07.2013 08:39: > Serhiy Storchaka, 29.07.2013 21:37: >> 29.07.13 20:19, Ian Kelly написав(ла): >>> On Mon, Jul 29, 2013 at 5:49 AM, Joshua Landau wrote: >>>> Also, couldn't Counter just extend from defaultdict? >>> >>> It could, but I expect the C helper function in 3.4 will be faster >>> since it doesn't even need to call __missing__ in the first place. >> >> I'm surprised, but the Counter constructor with commented out import of >> this accelerator is faster (at least for some data). > > Read my post. The accelerator doesn't take the fast path for dicts as > Counter is only a subtype of dict, not exactly a dict. That means that it > raises and catches a KeyError exception for each new value that it finds, > and that is apparently more costly than the overhead of calling get(). > > So, my expectation is that it's faster for highly repetitive data and > slower for mostly unique data. > > Maybe a "fast_dict_lookup" option for the accelerator that forces the fast > path would fix this. The Counter class, just like many (most?) other > subtypes of dict, definitely doesn't need the fallback behaviour.
Or rather drop the fallback path completely. It's not worth having code duplication if it's not predictable up-front (before looking at the data) if it will help or not. http://bugs.python.org/issue18594 Stefan -- http://mail.python.org/mailman/listinfo/python-list
