SWIG Python Examples

The following examples illustrate the use of SWIG with Python.

simple. A minimal example showing how SWIG can be used to wrap a C function, a global variable, and a constant.
constants. This shows how preprocessor macros and certain C declarations are turned into constants.
variables. An example showing how to access C global variables from Python.
value. How to pass and return structures by value.
class. Wrapping a simple C++ class.
reference. C++ references.
pointer. Simple pointer handling.
funcptr. Pointers to functions.

Compilation Issues

To create a Python extension, SWIG is run with the following options:
```
% swig -python interface.i
```
Please see the Windows page in the main manual for information on using the examples on Windows.

On Unix the compilation of examples is done using the file Example/Makefile. This makefile performs a manual module compilation which is platform specific. Typically, the steps look like this (Linux):

% swig -python interface.i
% gcc -fpic -c interface_wrap.c -I/usr/local/include/python1.5
% gcc -shared interface_wrap.o $(OBJS) -o interfacemodule.so 
% python
Python 1.5.2 (#3, Oct  9 1999, 22:09:34)  [GCC 2.95.1 19990816 (release)] on linux2
Copyright 1991-1995 Stichting Mathematisch Centrum, Amsterdam
>>> import interface
>>> interface.blah(...)
...

The politically "correct" way to compile a Python extension is to follow the steps described at www.python.org:
1. Create a file called Setup that looks like the following where $(SRCS) is filled in with any other source files you need to build the extension:
```
*shared*
interface interface_wrap.c $(SRCS)
```
2. Copy the file Makefile.pre.in from the Python distribution. Usually it's located in the directory /usr/local/lib/python1.5/config on a Unix machine.
3. Type the following to build the extension:
```
% make -f Makefile.pre.in boot
% make
```
4. And that's it. If you are preparing an extension for distribution, you may want to look at the distutils.

Compatibility

For Python 3, set the environment variable PY3=1. This will ensure the 2to3 program is run prior to running any example.

Your mileage may vary. If you experience a problem, please let us know by contacting us on the mailing lists.