# 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.