Python where we can, C ++ where we must

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Python where we can, C ++ where we must Source: http://xkcd.

1 Python where we can, C ++ where we must Source: Guy K. Kloss Python where we can,c++ where we must 1/28

2 Python where we can, C ++ where we must Guy K. Kloss BarCamp Auckland December 2007 Quote: Alex Martelli, Senior Google Developer Guy K. Kloss Python where we can,c++ where we must 2/28

3 Outline 1 Python 2 Extending/Integrating 3 A Real World Example 4 Tips Guy K. Kloss Python where we can,c++ where we must 3/28

4 Outline 1 Python 2 Extending/Integrating 3 A Real World Example 4 Tips Guy K. Kloss Python where we can,c++ where we must 4/28

5 What is Python? Object oriented Dynamic Easy to learn syntax High-level data types Scripting language Embeddable in C/C++ Guy K. Kloss Python where we can,c++ where we must 5/28

6 Python vs. Java (or C ++ ) No compilation Fast edit build debug cycle Dynamic Typing No need to declare variables for use Easy Syntax No curly braces, no semicolons, no new... Embeddable Scripting support for your applications Interactive Create, view, change objects at runtime 50% less code Compact and natural syntax 300% more productive Closer to the way you think Guy K. Kloss Python where we can,c++ where we must 6/28

7 Why Python? Mixable Extend Python with components written in C++, Java, C Embed Python into your application and call it from C/C++ Platform independent Powerful Ease of use of scripting language Built-in object types Extensive libraries Automatic memory management Modules, classes and exceptions Guy K. Kloss Python where we can,c++ where we must 7/28

8 What is Python used for? System Utilities System admin tools, portable shell scripts Internet Scripting CGI scripts, parse HTML, process XML, tools User Interfaces (UIs) & rapid prototyping Component Glue Scripting for apps, COM scripting Distributed Programming Web Services, COM, CORBA, XML RPC Database Programming Scientific Computing PyODE, NumPy, SciPy, PyMol,... Image Processing Python Image Library OpenGL Programming, Writing Games PyOpenGL, Panda3D, PyOgre, Py3d, VisualPython Artifical Intelligence Guy K. Kloss Python where we can,c++ where we must 8/28

9 Why Native Code? C/C++, Fortran (and Java, C #,...) Performance Binding to legacy code (Existing) Applications/Libraries want to be scripted... want to be tested... want to be re-used Guy K. Kloss Python where we can,c++ where we must 9/28

10 Outline 1 Python 2 Extending/Integrating 3 A Real World Example 4 Tips Guy K. Kloss Python where we can,c++ where we must 10/28

11 What if I could... Use this code more effectively...? [NaSt2D demonstration (native executable)] Guy K. Kloss Python where we can,c++ where we must 11/28

12 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 Python where we can,c++ where we must 12/28

13 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 Python where we can,c++ where we must 12/28

14 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 Python where we can,c++ where we must 12/28

15 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 Python where we can,c++ where we must 12/28

16 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 Python where we can,c++ where we must 12/28

17 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 Python where we can,c++ where we must 13/28

18 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 Python where we can,c++ where we must 13/28

19 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 Python where we can,c++ where we must 13/28

20 Hello World char const* greet(unsigned x) { static char const* const msgs[] = {"hello", "Boost.Python", "world!"}; if (x > 2) { } throw std::range error("greet: } return msgs[x]; Index out of range."); #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)... hello Boost.Python world! Guy K. Kloss Python where we can,c++ where we must 14/28

21 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 Python where we can,c++ where we must 15/28

22 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 Python where we can,c++ where we must 15/28

23 See it Happen I m making it work for you now... [ MyClass demonstration (MyClass.cpp, MyClass.h, mymodule.cpp)] Guy K. Kloss Python where we can,c++ where we must 16/28

24 Outline 1 Python 2 Extending/Integrating 3 A Real World Example 4 Tips Guy K. Kloss Python where we can,c++ where we must 17/28

25 A Real World Example Re-visiting NaSt2D Wrapping NaSt2D Control the code Guy K. Kloss Python where we can,c++ where we must 18/28

26 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 Python where we can,c++ where we must 19/28

27 Extend Wrapper Class Inheriting from C++ classes Interfacing numerical values Change functionality Follow the Computation Guy K. Kloss Python where we can,c++ where we must 20/28

28 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 Python where we can,c++ where we must 21/28

29 Do more Computations Parameter Study Change input file Compute several cases Plot results automatically Guy K. Kloss Python where we can,c++ where we must 22/28

30 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 Python where we can,c++ where we must 23/28

31 Outline 1 Python 2 Extending/Integrating 3 A Real World Example 4 Tips Guy K. Kloss Python where we can,c++ where we must 24/28

32 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 Python where we can,c++ where we must 25/28

33 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 Python where we can,c++ where we must 26/28

34 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 Python where we can,c++ where we must 27/28

35 Questions? Guy K. Kloss Python where we can,c++ where we must 28/28

Python Scripting for Computational Science

Hans Petter Langtangen Python Scripting for Computational Science Third Edition With 62 Figures 43 Springer Table of Contents 1 Introduction... 1 1.1 Scripting versus Traditional Programming... 1 1.1.1