Access to C functions from a python class using self ?

[christophe grimault]

To be more precise, the class Vector given in original posting is just 
here to explain the problem. In fact, the classes I use are signal 
processing classes, for example, a class 'SpectrumAnalyser' that has a 
method 'cross_periodogram' between to signal inputs is, for example, 
much closer to my real needs.

Such a class maintains state attritutes and arrays of preceding 
computations. They are part of *self in the C call, and I need to access 
them.

Previous answers, from thomas and giorgi, talking about

	PyObject_GetAttrString(self, "x1")

might be the kind of stuff I'm looking for. Are there any examples 
(source codes) using this, which i could analyse in order to figure out 
how this works with more complicated cases (tuples, Numpy arrays, ...)

Thanks in advance, to all

Bengt Richter wrote:

>On Mon, 30 Dec 2002 12:59:16 +0100, christophe grimault <christophe.grimault at novagrid.com> wrote:
>
>  
>
>>Hi there,
>>
>>I've been looking to 'ext & emb python', swig, cxx, ... for quite some 
>>time now, and I still can't figure out how to do the kind of stuff 
>>explained below...
>>
>>I define a class in python, let's say this simple class, just for the 
>>purpose of discussion :
>>
>>class Vector:
>>   def __init__(self, x1, x2, x3):
>>       self.x1, self.x2, self.x3 = x1, x2, x3
>>
>>   def sum(self):
>>       return self.x1 + self.x2 + self.x3
>>
>>Now, I find that sum is slow, and I want to speedup things by replacing 
>>sum by a call to C.
>>    
>>
>I suspect your best options will vary with your larger context. I.e.,
>when you "find that sum is slow," it was probably in a hot loop doing
>sum many times, or you wouldn't notice. So there is much else going on,
>and the actual summing may be the least of it (unless x1,x2,x3 are classes
>that define __add__ and contain large amounts of data to "add.") I'm
>assuming the x's are numbers.
>
>So what kind of loops do you have making use of this class Vector?
>
>  
>
>>Looking at the manual, I can write something like:
>>
>>static PyObject *sum( PyObject *self, PyObject *args )
>>
>>and  the manual tells me how to access elements passed in args, but does 
>>not tell how to access elements (in fact attributes) of self. How can I 
>>retrieve self.x1, self.x2, and self.x3 as defined in the python class 
>>    
>>
>>from *self passed to the C function ?
>  
>
>>The goal for me is to create classes quickly in Python. These classes 
>>    
>>
>This may become a goal, but IME it is ususally premature to say "the" goal
>while referring to a particular implementation strategy ;-)
>
>  
>
>>have, say, a constructor and 5 to 30 methods. The object itself is quite 
>>complex (lots of attributes of different types) and only one or two 
>>method need very high speed and thus, must call C.
>>    
>>
>I suspect there will be more than one way to accomplish this.
>
>  
>
>>And i want to avoid passing all the attributes needed by those C calls 
>>by increasing the *args !
>>
>>    
>>
>Ditto.
>
>Regards,
>Bengt Richter
>  
>

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