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-   -   Re: python 3 problem: how to convert an extension method into a classMethod (http://www.velocityreviews.com/forums/t958128-re-python-3-problem-how-to-convert-an-extension-method-into-a-classmethod.html)

 Peter Otten 02-27-2013 11:14 AM

Re: python 3 problem: how to convert an extension method into a classMethod

Robin Becker wrote:

> On 26/02/2013 18:38, Peter Otten wrote:
>> Robin Becker wrote:

> ...........3:
>>
>> \$ python -m timeit -s 'from new import instancemethod
>>> from math import sqrt
>>> class A(int): pass
>>> A.m = instancemethod(sqrt, None, A)
>>> a = A(42)
>>> ' 'a.m()'

>> 1000000 loops, best of 3: 0.5 usec per loop
>> \$ python -m timeit -s 'from math import sqrt
>>> class A(int):
>>> def m(self):
>>> return sqrt(self)
>>> a = A(42)
>>> ' 'a.m()'

>> 1000000 loops, best of 3: 0.473 usec per loop
>>
>>

> this analysis might be relevant if I wanted to use sqrt. However, in my
> case the method takes
>
>
>
> py C
> utf8 bytes 50 20 usec
> unicode 39 15
>
> here py refers to a native python method and C to the extension method
> after adding to the class. Both are called via an instance of the class.

I think you misunderstood. You compare the time it takes to run the function
coded in C and its Python equivalent -- that difference is indeed
significant.

But what I was trying to measure was the difference between two ways to wrap
the C function:

Given a function cfunc implemented in C and the two ways of turning it into
a method

(1)
class A(object):
pass

def method(self, ...):
return cfunc(self, ...)
A.method = method

(2)
class A(object):
pass

A.method = new.instancemethod(cfunc, None, A)

I interpreted my timeit results as an indication that both ways have roughly
the same overhead (method (1) being 0.027 usec faster).

I don't have your code available, that's why I picked math.sqrt as an
example for cfunc.

I expect that you will get a similar result with your actual cfunc and
therefore can (and should IMO) use method (1) in both Python 2 and 3
-- but of course not being able to measure it myself it may turn out I'm
wrong.

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