On Nov 14, 2012, at 5:37 PM, Chris Withers wrote:
> On 14/11/2012 10:11, mar...@v.loewis.de wrote:
>>
>> Zitat von Chris Withers <ch...@simplistix.co.uk>:
>>
>>> a_dict = dict(
>>> x = 1,
>>> y = 2,
>>> z = 3,
>>> ...
>>> )
>>
>>> What can we do to speed up the former case?
>>
>> It should be possible to special-case it. Rather than creating
>> a new dictionary from scratch, one could try to have the new dictionary
>> the same size as the original one, and copy all entries.
>
> Indeed, Doug, what are your views on this? Also, did you have a real-world
> example where this speed difference was causing you a problem?
No, not particularly. I noticed people using dict() and wondered what impact it
might have in a general case.
>
>> I don't know how much this would gain, though. You still have to
>> create two dictionary objects. For a better speedup, try
>>
>> def xdict(**kwds):
>> return kwds
>
> Hah, good call, this trumps both of the other options:
>
> $ python2.7 -m timeit -n 1000000 -r 5 -v
> "{'a':1,'b':2,'c':3,'d':4,'e':5,'f':6,'g':7}"
> raw times: 1.45 1.45 1.44 1.45 1.45
> 1000000 loops, best of 5: 1.44 usec per loop
> $ python2.6 -m timeit -n 1000000 -r 5 -v 'dict(a=1,b=2,c=3,d=4,e=5,f=6,g=7)'
> raw times: 2.37 2.36 2.36 2.37 2.37
> 1000000 loops, best of 5: 2.36 usec per loop$ python2.6 -m timeit -n 1000000
> -r 5 -v 'def md(**kw): return kw; md(a=1,b=2,c=3,d=4,e=5,f=6,g=7)'
> raw times: 0.548 0.533 0.55 0.577 0.539
> 1000000 loops, best of 5: 0.533 usec per loop
>
> For the naive observer (ie: me!), why is that?
>
> Chris
>
> --
> Simplistix - Content Management, Batch Processing & Python Consulting
> - http://www.simplistix.co.uk
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