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Currying with instancemethod (was Re: [Python-Dev] accumulator display syntax)

Alex Martelli aleaxit at yahoo.com
Fri Oct 17 18:05:24 EDT 2003 
On Friday 17 October 2003 11:45 pm, Phillip J. Eby wrote:
   ...
> At 10:40 PM 10/17/03 +0200, Alex Martelli wrote:
> >Yes, def curry(func, arg): return new.instancemethod(func, arg, object)
   ...
> >def curry(func, arg):
> >     def curried(*args): return func(arg, *args)
> >     return curried
   ...
> It is a big win if the curried function will be used in a
> performance-sensitive way.  Instance method objects don't pay for setting
> up an extra frame object, and for the single curried argument, the
> interpreter even shortcuts some of the instancemethod overhead!  So, if I

You're right: the instancemethod version has impressively better performance
(should the curried function be used in a bottleneck, of course) -- i.e., 
given a.py:

import new

def curry1(func, arg):
    return new.instancemethod(func, arg, object)

def curry2(func, arg):
    def curried(*args): return func(args, *args)
    return curried

def f(a, b, c): return a, b, c

I've measured:

[alex at lancelot ba]$ timeit.py -c -s'
import a
g = a.curry2(a.f, 23)
' 'g(45, 67)'
100000 loops, best of 3: 2 usec per loop

[alex at lancelot ba]$ timeit.py -c -s'
import a
g = a.curry1(a.f, 23)
' 'g(45, 67)'
1000000 loops, best of 3: 1.09 usec per loop

I sure didn't expect an almost 2:1 ratio, while you did predict it.


Alex
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