Specific question about C callback with Python handler ...

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Specific question about C callback with Python handler ...

by Sandy Walsh :: Rate this Message:

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Hi,

I have a C library which generates a Callback that I want to handle in
my Python code.

My .i file essentially looks like this, where I register my DataCallback
via the Start() function:

----------
%module probe
%{
#include "cheader.h"
%}

typedef void (*DataCallBack)(char*, unsigned int, int);

int Start(DataCallBack);
----------

My Python code essentially looks like this:

----------
import probe

def ProbeCallback(a, b, c):
# char*, unsigned int, int
print "PYTHON Callback!"

probe.Start(ProbeCallback)
----------

But when I run the Python code, it can't coerce ProbeCallback to be a
DataCallback. I get the following exception:

Traceback (most recent call last):
File "TestProbe.py", line ## in <module>
probe.Start(ProbeCallback)
TypeError: in method 'Start', argument 1 of type 'DataCallBack'

Any idea what I'm missing here?

Additionally, I've tried wrapping the Start function with my old
Callback registration/invocation system. In this case the C callback
gets called successfully, I can assemble the argument tuple to call the
Python Callback. The Python Callback is considered a proper "callable"
object, but it exceptions deep in Swig on invocation. I suspect it's the
same reason the above Cast Exception check is being generated.

Thanks in advance,
Sandy

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Re: SOLVED: Specific question about C callback with Python handler ...

by Sandy Walsh :: Rate this Message:

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Found the problem. Full writeup of problem and solution can be found here:

http://sandywalsh.blogspot.com/2009/10/interfacing-multi-threaded-c-apis-with.html

Cheers,
Sandy

Sandy Walsh wrote:
> Hi,
>
> I have a C library which generates a Callback that I want to handle in
> my Python code.
>

[swalsh.vcf]