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To: python-list@python.org
From: Peter Otten <__peter__@web.de>
Subject: Re: python 3 problem: how to convert an extension method into a class Method
Date: Tue, 26 Feb 2013 19:38:44 +0100
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References: <512CEF0C.3020906@chamonix.reportlab.co.uk>
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Robin Becker wrote:

> In python 2 I was able to improve speed of reportlab using a C extension
> to optimize some heavily used methods.
> 
> so I was able to do this
> 
> 
> class A:
>      .....
>      def method(self,...):
>         ....
> 
> 
> try:
>      from extension import c_method
>      import new
>      A.method = new.instancemethod(c_method,None,A)
> except:
>      pass
> 
> and if the try succeeds our method is bound as a class method ie is
> unbound and works fine when I call it.
> 
> In python 3 this doesn't seem to work at all. In fact the new module is
> gone. The types.MethodType stuff doesn't seem to work.
> 
> Is there a way in Python 3.3 to make this happen? This particular method
> is short, but is called many times so adding python wrapping layers is not
> a good way forward.
> 
> If the above cannot be made to work (another great victory for Python 3)
> then is there a way to bind an external method to the instance without
> incurring too much overhead.

Hm, according to my random measurement your clever approach incurs more 
overhead than the straight-forward way that continues to work in Python 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