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Re: Passing pointer to array from C to Python..and modifying same array in python?

 
 
J W
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      07-14-2003
Hi David (and all membors of this list):

Thank you so much for your advice.

I have a few follow-up questions.

1) when you say to "have the C function construct a
new python object (i.e. the "wrapper")",
what type of python object would it be:
PyLong, PyObject, PyCobject (not exactly sure what
this is, but i've seen this in literature), or
something else?

2) When you say "
> The get method should take self and the array
> index as paramaters and return the values in that

slot of the array",

Do I use the "PyArg_ParseTuple" funciton call in the
"get()" method? If so, what parameters am I using to
indicate object type?
Is it correct to assume that the keyword "_self_" is
actually seen in Python, and not the C extension
object?
In the C- extension function, what type of object is
"_self_" -- PyLong, PyObject?


Thanks again


--- David Jeske <(E-Mail Removed)> wrote:
> On Fri, Jul 11, 2003 at 02:06:10PM -0700, JW wrote:
> > I have an array (presumably 'large') that is

> mallocced in a C
> > function and its values are initialized in that

> same function. I
> > would like to pass just the pointer to the

> beginning of the array
> > from this C function to a Pyton function. Then

> the python method
> > can individually access and MODIFY individual

> members of the array.
> > After the call to the python method, the C

> function will see any
> > changes to the array.

>
> > Can this be done?

>
> Of course this can be done, and there are a number
> of ways to do
> it. Based on your implication that there are many
> more values put in
> the array by the C code than will be accessed (or
> changed) by the
> Python code, this method might make sense:
>
> 1) have the C function construct a new python object
> (i.e. the "wrapper")
>
> 2) put the real pointer to the C array into the
> wrapper as instance data
>
> 3) register two methods for the object "get()" and
> "set()", impelemented
> in C as Python exported functions.
>
> The get method should take self and the array
> index as paramaters and
> return the values in that slot of the array
>
> The set method should take self, an index, and
> the values as paramaters
> and it should modify the real "C-version" of the
> array.
>
> 4) when you execute your python function, it will be
> given this
> "wrapper" object as a paramater. It can then call
> into the methods in
> the wrapper object to access and change the
> C-array "in-place" without
> converting it at all. Each new value which is set
> into the array
> is converted on the fly.
>
> 5) If you like, you can convert get() and set() to
> __get__() and __set__
> so you can use array access syntax to access the
> array from python.
>
>
> --
> David Jeske (N9LCA) + http://www.chat.net/~jeske/ +

http://www.velocityreviews.com/forums/(E-Mail Removed)


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