Thinking Hybrid - Python/C++ Integration

Python Extending/Integrating A Real World Example Tips Summary

Python where we can,C++ where we must

Source:http://xkcd.com/413/

Guy K. Kloss | Thinking Hybrid – Python/C++ Integration 1/33

http://xkcd.com/413/


Thinking Hybrid –Python/C++ Integration

(Python where we can, C++ where we must∗)

Guy K. Kloss

Computer ScienceMassey University, Albany

Computer Science/Information Technology SeminarAuckland, 23 April 2008

∗ Quote: Alex Martelli, Senior Google DeveloperGuy K. Kloss | Thinking Hybrid – Python/C++ Integration 2/33


Outline

1 Python

2 Extending/Integrating

3 A Real World Example

4 Tips



Outline

1 Python



4 Tips



Why Python?

Python C/C++• dynamic • static• 50% less code, 300% pro-ductivity

• high performance

• extendable with C/C++ • extendable with Python• platform independent • close to hardware• garbage collector • small memory footprint• huge standard library• many other bindings

While others are still debugging, you can publish your results!



Why Python?

Source: http://xkcd.com/371/




What is Python used for?

System UtilitiesSystem admin tools, portable shell scriptsInternet ScriptingCGI scripts, parse HTML, process XML, email toolsUser Interfaces (UIs) & rapid prototypingComponent GlueScripting for apps, COM scriptingDistributed ProgrammingWeb Services, COM, CORBA, XML–RPCDatabase ProgrammingScientific ComputingPyODE, NumPy, SciPy, PyMol, . . .Image ProcessingPython Image Library, OpenCVOpenGL Programming, Writing GamesPyOpenGL, Panda3D, PyOgre, Py3d, VisualPythonArtifical Intelligence



Outline

1 Python



4 Tips



Extending/Integrating



What if I could . . .

Use this code more effectively . . . ?

[NaSt2D demonstration (native executable)]



Extending/Integration

The Contestants:The “classic way” . . .Extending and Embedding the Python InterpreterThe “new way” . . .Python ctypes

SWIGBoost.PythonOthers:

SIPPythonizerSILOON(Pyrex)

Extensions also for Java, C#, Fortran, . . . availableGuy K. Kloss | Thinking Hybrid – Python/C++ Integration 12/33


Boost.Python

Thinking Hybrid with Boost.PythonBottom up and . . .Top down possibleDevelop quicklyResolve bottle necksDonald Knuth’s:“Premature optimisation is the root of all evil.”or: Don’t Optimise Now!



Elegantly withBoost.Python



Hello World

char const* greet(unsigned x) {static char const* const msgs[] = {"hello", "Boost.Python", "world!"};if (x > 2) {

throw std::range error("greet: Index out of range.");}return msgs[x];

}

#include <boost/python.hpp>using namespace boost::python;BOOST PYTHON MODULE(hello){

def("greet", greet, "return one of 3 parts of a greeting");}

And here it is in action:>>> import hello>>> for x in range(3):... print hello.greet(x)...helloBoost.Pythonworld!



Boost.Python

One of a few libraries that make it easyto integrate C++ and Python codeHow does it pull off this trick?Template meta–programming(i. e. Don’t ask!)



See it Happen

I’m making it work for you now . . .

[“MyClass” demonstration (MyClass.cpp, MyClass.h, mymodule.cpp)]



Outline

1 Python



4 Tips



Real–WorldExamples



A Real World ExampleRe-visiting NaSt2D

Wrapping NaSt2DControl the code



NaSt2D in Python

This is what I’m going to show you:Code to be wrappedGenerated wrapper codeGenerator scriptSCons (build system)How it works with Python

[Wrapped NaSt2D demonstration (Wrapper.h, nast2dmodule.cpp,

generate bindings.py, SConstruct, demo0.py)]



Extend Wrapper Class

Inheriting from C++ classesInterfacing numerical valuesChange functionalityFollow the Computation



Overriding in Python

This is what I’m going to show you:Overriding a native method in PythonNative method needs to be “virtual”Live data plotting with GNUplot

[NaSt2D with plotting demonstration (demo1.py, demo2.py)]



Do more Computations

Parameter StudyChange input fileCompute several casesPlot results automatically



Automating in Python

This is what I’m going to show you:Using a template input fileBatch–calculating several runsPlotting results with GNUplot

[NaSt2D with parameter variation demonstration (demo3.py, demo4.py)]



Outline

1 Python



4 Tips



Some Tips . . .Guy K. Kloss | Thinking Hybrid – Python/C++ Integration 27/33


Tips

To override C++ methods: make them virtualC/C++ pit fall

Call by reference/valueSolution: calling policies

Map to “other/sane” languagesJava: JythonC#: IronPythonFortran: PyFort, Py2F(Native to other: SWIG)



Summary

Why is Python good for you?How can performance bottle necks be resolved?Advantages of “Thinking Hybrid”Python–native wrapping using Boost.PythonAutomated wrapper generationSCons build system



Python and the “Need for Speed”

Cuong Do – Software Architect YouTube.com“Python is fast enough for our site

and allows us to produce maintainable featuresin record times,

with a minimum of developers.”



Some Links

Boost.Pythonhttp://www.boost.org/libs/python/doc/

Py++http://www.language-binding.net/pyplusplus/pyplusplus.html

SConshttp://www.scons.org/

NaSt2Dftp://ftp.lrz-muenchen.de/pub/science/fluiddynamics/cfd/NaSt2Dhttp://people.scs.fsu.edu/~burkardt/cpp_src/nast2d/nast2d.htmlhttp://home.arcor.de/drklaus.bauerfeind/nast/eNaSt2D.html


http://www.boost.org/libs/python/doc/

http://www.language-binding.net/pyplusplus/pyplusplus.html

http://www.language-binding.net/pyplusplus/pyplusplus.html

http://www.scons.org/

ftp://ftp.lrz-muenchen.de/ pub/ science/ fluiddynamics/ cfd/ NaSt2D

ftp://ftp.lrz-muenchen.de/ pub/ science/ fluiddynamics/ cfd/ NaSt2D

http://people.scs.fsu.edu/ ~burkardt/ cpp_src/ nast2d/ nast2d.html

http://people.scs.fsu.edu/ ~burkardt/ cpp_src/ nast2d/ nast2d.html

http://home.arcor.de/ drklaus.bauerfeind/ nast/ eNaSt2D.html

http://home.arcor.de/ drklaus.bauerfeind/ nast/ eNaSt2D.html


Questions?

[email protected] and code available here:http://www.kloss-familie.de/moin/TalksPresentations


[email protected]

http://www.kloss-familie.de/moin/TalksPresentations

Thinking Hybrid - Python/C++ Integration

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