| <html> |
| <head> |
| <title>SWIG:Examples:python:class</title> |
| </head> |
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| <body bgcolor="#ffffff"> |
| |
| |
| <tt>SWIG/Examples/python/class/</tt> |
| <hr> |
| |
| <H2>Wrapping a simple C++ class</H2> |
| |
| <p> |
| This example illustrates wrapping a simple C++ class to give a Python class. |
| |
| <h2>The C++ Code</h2> |
| |
| Suppose you have some C++ classes described by the following (and admittedly lame) |
| header file: |
| |
| <blockquote> |
| <pre> |
| /* File : example.h */ |
| |
| class Shape { |
| public: |
| Shape() { |
| nshapes++; |
| } |
| virtual ~Shape() { |
| nshapes--; |
| } |
| double x, y; |
| void move(double dx, double dy); |
| virtual double area() = 0; |
| virtual double perimeter() = 0; |
| static int nshapes; |
| }; |
| |
| class Circle : public Shape { |
| private: |
| double radius; |
| public: |
| Circle(double r) : radius(r) { } |
| virtual double area(); |
| virtual double perimeter(); |
| }; |
| |
| class Square : public Shape { |
| private: |
| double width; |
| public: |
| Square(double w) : width(w) { } |
| virtual double area(); |
| virtual double perimeter(); |
| }; |
| </pre> |
| </blockquote> |
| |
| <h2>The SWIG interface</h2> |
| |
| A simple SWIG interface for this can be built by simply grabbing the header file |
| like this: |
| |
| <blockquote> |
| <pre> |
| /* File : example.i */ |
| %module example |
| |
| %{ |
| #include "example.h" |
| %} |
| |
| /* Let's just grab the original header file here */ |
| %include "example.h" |
| </pre> |
| </blockquote> |
| |
| Note: when creating a C++ extension, you must run SWIG with the <tt>-c++</tt> option like this: |
| <blockquote> |
| <pre> |
| % swig -c++ -python example.i |
| </pre> |
| </blockquote> |
| |
| <h2>A sample Python script</h2> |
| |
| Click <a href="runme.py">here</a> to see a script that calls the C++ functions from Python. |
| |
| <h2>Key points</h2> |
| |
| <ul> |
| <li>To create a new object, you call a constructor like this: |
| |
| <blockquote> |
| <pre> |
| c = example.new_Circle(10.0) |
| </pre> |
| </blockquote> |
| |
| <p> |
| <li>Member variables of the C++ class are wrapped as attributes of the Python class. |
| For example: |
| |
| <blockquote> |
| <pre> |
| c.x = 15 # Set member data |
| x = c.x # Get member data |
| </pre> |
| </blockquote> |
| |
| <p> |
| <li>Member function are invoked as you would expect: |
| |
| <blockquote> |
| <pre> |
| print "The area is ", c.area() |
| </pre> |
| </blockquote> |
| |
| <p> |
| <li>To invoke a destructor, simply call <code>del</code> on the object: |
| |
| <blockquote> |
| <pre> |
| del c # Deletes a shape |
| </pre> |
| </blockquote> |
| |
| <p> |
| <li>Static member variables are wrapped as C global variables. For example: |
| |
| <blockquote> |
| <pre> |
| n = example.cvar.Shape_nshapes # Get a static data member |
| example.cvar.Shapes_nshapes = 13 # Set a static data member |
| </pre> |
| </blockquote> |
| |
| </ul> |
| |
| <h2>General Comments</h2> |
| |
| <ul> |
| <li>SWIG <b>does</b> know how to properly perform upcasting of objects in |
| an inheritance hierarchy (including multiple inheritance). Therefore |
| it is perfectly safe to pass an object of a derived class to any |
| function involving a base class. |
| |
| <li>C++ Namespaces - %nspace isn't yet supported for Python. |
| |
| </ul> |
| |
| <hr> |
| </body> |
| </html> |
