Talk given at the January 2008 meeting of the New Zealand Python User Group in Auckland. Outline: Talk on integrating native C++ sensibly into Python for ease of use of the code base. Inheriting from C++ classes, overriding functionality, automatically generating the bindings using Py++ and SCons. Code demonstrated in the presentation can be found here: http://www.kloss-familie.de/moin/TalksPresentations

1. Python Extending/Integrating A Real World Example Tips Summary
Python where we can,
C++ where we must
Source: http://xkcd.com/353/
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 1/25

2. Python Extending/Integrating A Real World Example Tips Summary
Thinking Hybrid –
Python/C++ Integration
(Python where we can, C++ where we must∗ )
Guy K. Kloss
New Zealand Python User Group Meeting
Auckland, 30 January 2008
∗ Quote: Alex Martelli, Senior Google Developer
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 2/25

3. Python Extending/Integrating A Real World Example Tips Summary
Outline
1 Python
2 Extending/Integrating
3 A Real World Example
4 Tips
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 3/25

4. Python Extending/Integrating A Real World Example Tips Summary
Outline
1 Python
2 Extending/Integrating
3 A Real World Example
4 Tips
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 4/25

5. Python Extending/Integrating A Real World Example Tips Summary
Why Python?
We all know why . . .
Some reasons that are important for us:
Dynamic
High-level data types
Embeddable/Mixable
Extend Python with components
written in C++, Java, C
Embed Python into your application
and call it from C/C++
Platform independent
50 % less code, 300 % more productive
Automatic memory management
All those utilities, modules, . . .
Many, many more reasons . . .
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 5/25

6. Python Extending/Integrating A Real World Example Tips Summary
Why Python?
Source: http://xkcd.com/371/
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 6/25

7. Python Extending/Integrating A Real World Example Tips Summary
Outline
1 Python
2 Extending/Integrating
3 A Real World Example
4 Tips
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 7/25

8. Python Extending/Integrating A Real World Example Tips Summary
What if I could . . .
Use this code more effectively . . . ?
[NaSt2D demonstration (native executable)]
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 8/25

9. Python Extending/Integrating A Real World Example Tips Summary
Extending/Integration
The Contestants:
The “classic way” . . .
Extending and Embedding the Python Interpreter
The “new way” . . .
Python ctypes
SWIG
Boost.Python
Others:
SIP
Pythonizer
SILOON
(Pyrex)
Extensions also for Java, C#, Fortran, . . . available
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 9/25

10. Python Extending/Integrating A Real World Example Tips Summary
Extending/Integration
The Contestants:
The “classic way” . . .
Extending and Embedding the Python Interpreter
The “new way” . . .
Python ctypes
SWIG
Boost.Python
Others:
SIP
Pythonizer
SILOON
(Pyrex)
Extensions also for Java, C#, Fortran, . . . available
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 9/25

11. Python Extending/Integrating A Real World Example Tips Summary
Extending/Integration
The Contestants:
The “classic way” . . .
Extending and Embedding the Python Interpreter
The “new way” . . .
Python ctypes
SWIG
Boost.Python
Others:
SIP
Pythonizer
SILOON
(Pyrex)
Extensions also for Java, C#, Fortran, . . . available
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 9/25

12. Python Extending/Integrating A Real World Example Tips Summary
Extending/Integration
The Contestants:
The “classic way” . . .
Extending and Embedding the Python Interpreter
The “new way” . . .
Python ctypes
SWIG
Boost.Python
Others:
SIP
Pythonizer
SILOON
(Pyrex)
Extensions also for Java, C#, Fortran, . . . available
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 9/25

13. Python Extending/Integrating A Real World Example Tips Summary
Extending/Integration
The Contestants:
The “classic way” . . .
Extending and Embedding the Python Interpreter
The “new way” . . .
Python ctypes
SWIG
Boost.Python
Others:
SIP
Pythonizer
SILOON
(Pyrex)
Extensions also for Java, C#, Fortran, . . . available
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 9/25

14. Python Extending/Integrating A Real World Example Tips Summary
Boost.Python
Thinking Hybrid with Boost.Python
Bottom up and . . .
Top down possible
Develop quickly
Resolve bottle necks
Donald Knuth’s:
“Premature optimisation is the root of all evil.”
or: Don’t Optimise Now!
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 10/25

15. Python Extending/Integrating A Real World Example Tips Summary
Boost.Python
Thinking Hybrid with Boost.Python
Bottom up and . . .
Top down possible
Develop quickly
Resolve bottle necks
Donald Knuth’s:
“Premature optimisation is the root of all evil.”
or: Don’t Optimise Now!
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 10/25

16. Python Extending/Integrating A Real World Example Tips Summary
Boost.Python
Thinking Hybrid with Boost.Python
Bottom up and . . .
Top down possible
Develop quickly
Resolve bottle necks
Donald Knuth’s:
“Premature optimisation is the root of all evil.”
or: Don’t Optimise Now!
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 10/25

17. Python Extending/Integrating A Real World Example Tips Summary
Hello World
char const* greet(unsigned x) {
static char const* const msgs[] = {quot;helloquot;, quot;Boost.Pythonquot;,
quot;world!quot;};
if (x > 2) {
throw std::range error(quot;greet: Index out of range.quot;);
}
return msgs[x];
}
#include <boost/python.hpp>
using namespace boost::python;
BOOST PYTHON MODULE(hello)
{
.def(quot;greetquot;, greet, quot;return one of 3 parts of a greetingquot;);
}
And here it is in action:
>>> import hello
>>> for x in range (3):
... print hello . greet ( x )
...
hello
Boost . Python
world !
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 11/25

18. Python Extending/Integrating A Real World Example Tips Summary
Boost.Python
One of a few libraries that make it easy
to integrate C++ and Python code
How does it pull off this trick?
Template meta–programming
(i. e. Don’t ask!)
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 12/25

19. Python Extending/Integrating A Real World Example Tips Summary
Boost.Python
One of a few libraries that make it easy
to integrate C++ and Python code
How does it pull off this trick?
Template meta–programming
(i. e. Don’t ask!)
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 12/25

20. Python Extending/Integrating A Real World Example Tips Summary
See it Happen
I’m making it work for you now . . .
[“MyClass” demonstration (MyClass.cpp, MyClass.h, mymodule.cpp)]
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 13/25

21. Python Extending/Integrating A Real World Example Tips Summary
Outline
1 Python
2 Extending/Integrating
3 A Real World Example
4 Tips
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 14/25

22. Python Extending/Integrating A Real World Example Tips Summary
A Real World Example
Re-visiting NaSt2D
Wrapping NaSt2D
Control the code
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 15/25

23. Python Extending/Integrating A Real World Example Tips Summary
NaSt2D in Python
This is what I’m going to show you:
Code to be wrapped
Generated wrapper code
Generator script
SCons (build system)
How it works with Python
[Wrapped NaSt2D demonstration (Wrapper.h, nast2dmodule.cpp,
generate bindings.py, SConstruct, demo0.py)]
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 16/25

24. Python Extending/Integrating A Real World Example Tips Summary
Extend Wrapper Class
Inheriting from C++ classes
Interfacing numerical values
Change functionality
Follow the Computation
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 17/25

25. Python Extending/Integrating A Real World Example Tips Summary
Overriding in Python
This is what I’m going to show you:
Overriding a native method in Python
Native method needs to be “virtual”
Live data plotting with GNUplot
[NaSt2D with plotting demonstration (demo1.py, demo2.py)]
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 18/25

26. Python Extending/Integrating A Real World Example Tips Summary
Do more Computations
Parameter Study
Change input file
Compute several cases
Plot results automatically
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 19/25

27. Python Extending/Integrating A Real World Example Tips Summary
Automating in Python
This is what I’m going to show you:
Using a template input file
Batch–calculating several runs
Plotting results with GNUplot
[NaSt2D with parameter variation demonstration (demo3.py, demo4.py)]
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 20/25

28. Python Extending/Integrating A Real World Example Tips Summary
Outline
1 Python
2 Extending/Integrating
3 A Real World Example
4 Tips
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 21/25

29. Python Extending/Integrating A Real World Example Tips Summary
Tips
To override C++ methods: make them virtual
C/C++ pit fall
Call by reference/value
Solution: calling policies
Map to “other/sane” languages
Java: Jython
C#: IronPython
Fortran: PyFort, Py2F
(Native to other: SWIG)
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 22/25

30. Python Extending/Integrating A Real World Example Tips Summary
Summary
Why is Python good for you?
How can performance bottle necks be resolved?
Advantages of “Thinking Hybrid”
Python–native wrapping using Boost.Python
Automated wrapper generation
SCons build system
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 23/25

31. Python Extending/Integrating A Real World Example Tips Summary
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 features
in record times,
with a minimum of developers.”
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 24/25

32. Python Extending/Integrating A Real World Example Tips Summary
Questions?
G.Kloss@massey.ac.nz
Slides and code available here:
http://www.kloss-familie.de/moin/TalksPresentations
Guy K. Kloss — Thinking Hybrid – Python/C++ Integration 25/25