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Storing objects required by functions.

Bengt Richter bokr at oz.net
Tue Dec 30 23:07:01 EST 2003 
On Wed, 31 Dec 2003 04:04:47 +0200, Christos "TZOTZIOY" Georgiou <tzot at sil-tec.gr> wrote:

>On 31 Dec 2003 00:08:47 GMT, rumours say that bokr at oz.net (Bengt
>Richter) might have written:
>
>>The other way is to take advantage of functions' roles as decriptors and the mechanism that
>>makes bound methods with a self as the first arg, but the rest apparently normal. I.e,
>>we can put the r parameter in the place of self (not specifically tested)
>>
>>    def uses_self(r, x):
>>        pass
>>    uses_self = uses_self.__get__(re.compile("..."))
>
>It's much more general to use new.instancemethod.  See:
I think I did use new.instancemethod, through another door ;-)

 >>> def uses_self(r, x):
 ...     pass
 ...
 >>> import re
 >>> uses_self = uses_self.__get__(re.compile("..."))
 >>> type(uses_self)
 <type 'instancemethod'>

 >>> myim = type(uses_self)
 >>> myim
 <type 'instancemethod'>

 >>> import new
 >>> myim is new.instancemethod
 True
;-)

 >>> def foo(self, *args, **kw): print 'self=%r, args=%r, kw=%r'%(self, args, kw)
 ...
 >>> myim(foo, 'dummy self', object) # object per your usage
 <bound method object.foo of 'dummy self'>
 >>> foom = myim(foo, 'dummy self', object) # object per your usage
 >>> foom(1,2,3,hi='Hello')
 self='dummy self', args=(1, 2, 3), kw={'hi': 'Hello'}

I didn't make voodoo out of it though. Interesting, but all that nested
calling at call-time seems like it would make for a performance hit? Unless maybe it is
all packed up in slots that C can get to very fast??

>
>def voodoo(function, *its_arguments):
>    from new import instancemethod
>    def child(function, first_argument, *rest_of_arguments):
>        if rest_of_arguments:
>            return child(
>                instancemethod(function, first_argument, object),
>                *rest_of_arguments
>            )
>        else:
>            return instancemethod(function, first_argument, object)
>    return child(function, *its_arguments)
>
>The import statement is in the voodoo just for completeness including it
>here.
>The function above recurses in order to allow stuff like:
>
>getter = voodoo(getattr, my_object, "its_attribute")
>
>or the more modern
>
>getter = voodoo(operator.itemgetter("its_attribute"), my_object)
>
>and similarly
>
>setter = voodoo(operator, my_object, "its_attribute")
>
>allowing
>
>setter(value)
>
>at good speeds.
>
>
>I have a module predicates.py defining All and Any classes for
>iterables, and the trick above plus itertools allows *some* operations
>to run faster than correspondent python code...
Interesting. Gotta go.

Regards,
Bengt Richter
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