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

Discussion in 'Python' started by Peter Otten, Feb 26, 2013.

  1. Peter Otten

    Peter Otten Guest

    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
    Peter Otten, Feb 26, 2013
    #1
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