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Python, C++ interaction

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  Python, C++ interaction Michael Kreim <michael@perfect-kreim.de> - 2014-12-03 09:29 +0100
    Re: Python, C++ interaction Christian Gollwitzer <auriocus@gmx.de> - 2014-12-04 09:49 +0100

#81847 — Python, C++ interaction

Hi,

we are working on a small scientific program that helps us in developing 
and testing of new numerical methods for a certain type of biochemical 
problems. I spare you the math ;-)

We code our new methods in Python and compare them with the existing 
methods. Unfortunately, these existing methods are quite slow and need a 
lot of runtime. Therefor we implemented them in C++.

Now, we like to combine these two approaches. So we can develop a new 
method in Python and compare it easily with the results from the C++ 
functions.

I did some googleing on extending Python by C++ code but I did not find 
something that satisfies me. I gave SWIG a try, but several webpages 
disadvised me of using it. Also my small experiments did not work. Now, 
I read about ctypes. But as far as I understood it, I have to write a C 
wrapper for my C++ code and then a Python wrapper for my C code. That 
seems a little complicated.

My C++ code is structured as a class that contains several variables and 
functions. Then everything is compiled as a shared library. I can write 
things like:

MyClass.initialvalue = 5;
MyClass.timestep = 0.1;
...
MyClass.solve();

I would like to keep this structure in python, but if I understand 
ctypes correctly I would loose the class approach.

So after the long writeup I come to my questions:

What are you using to wrap C++ classes for Python?
Can you recommend swig? Should I give it another try?
Did I misunderstood ctypes?

Also later on in our code development we would like to pass python 
lambda functions to C++. So far I understood that this seems not to be 
possible. Do you have any ideas or hints on this topics?

Thank you very much.

Cheers,

Michael

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#81885

Am 03.12.14 09:29, schrieb Michael Kreim:
> I did some googleing on extending Python by C++ code but I did not find
> something that satisfies me. I gave SWIG a try, but several webpages
> disadvised me of using it. Also my small experiments did not work.

I don't know why SWIG is discouraged; in my experience, it is a very 
easy way to generate the wrapping code around C++ classes, and also 
flexible in many directions. It can be easily extended for new datatypes 
(there is a numpy interface module, for instance), and also generates 
code for other scripting languages as well. What specifically did you 
try, and what failed?

Concerning the callbacks, I don't know about these, but hopefully you 
are aware that you can easily loose the C++ speed advantage by using 
Python lambdas, since those have to go through the Python interpreter.

	Christian

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