SWIG

Links

Install

Download and extract swigwin-1.3.31.zip from http://www.swig.org/download.html (Note: This is a development release).

I installed to:

C:\bin\swigwin-1.3.31\

Documentation

Can be found in the installation folder:

Notes	Folder
Python Examples	`Examples/python/index.html`
Windows documentation	`Doc/Manual/Windows.html`

Setup

Create the following environment variables:

SET PYTHON_INCLUDE=C:\tools\Python25\include
SET PYTHON_LIB=C:\tools\Python25\libs\python25.lib

Add the SWIG folder to your PATH (so swig.exe can be found):
```
SET PATH=%PATH%;C:\bin\swigwin-1.3.31;
```
The python-swig.bat batch file will set-up these variables for you.

Project

Interface Definition

Create an interface definition file for your class e.g for a Client class:

/* File : sample.i */
%module sample

%{
#include "Client.h"
%}

%include "std_string.i"
/* Let's just grab the original header file here */
%include "Client.h"

The %module line specifies the name under which you are going to import the resulting extension module in Python.
The block between the “%\{” and the “%\}” is copied into the generated wrapper as is.
%include "std_string.i" is a special SWIG header which allows us to pass python string to std::string arguments. Other headers can be included for maps, lists, etc… See the SWIG, STL/C++ Library notes.

Note: I think we need to include the header before the class is included.
SWIG will parse the declarations in the file Client.h. You can refer to any number of header files.

Custom Build Step

In Microsoft Visual Studio, right click on the interface definition file, select Properties, then Custom Build Step, General. Click on the ... button to the right of Command Line and enter the following:

echo In order to function correctly, please ensure the following environment variables are correctly set:
echo PYTHON_INCLUDE: %PYTHON_INCLUDE%
echo PYTHON_LIB: %PYTHON_LIB%
echo on
swig -c++ -python $(InputPath)

In the Outputs control, enter:
```
$(InputName)_wrap.cxx
```
Click OK to save the settings (there are no Additional Dependencies).
Build the solution, then add the generated source file e.g. sample_wrap.cxx to the project.
If you try and build the project now, you will probably get an error like this:
```
Error  1  fatal error C1083: Cannot open include file: 'Python.h': No such file or directory
```
Follow the next steps to set-up the Visual Studio Environment.

Visual Studio Environment

Change the project configuration to Release (the default installation of python does not include include the debug libraries).
Right click on the project, and select Properties, Configuration Properties, General. Change Configuration Type to Dynamic Library (.dll).
Right click on the project, and select Properties, Configuration Properties, C/C++, General. In Additional Include Directories enter:
```
$(PYTHON_INCLUDE)
```
Right click on the project, and select Properties, Configuration Properties, Linker, General. In the Output File enter the DLL name you want created e.g:
```
_sample.pyd
```
Note: the underscore is important. The actual extension module (in this example) will be sample.py, which in turn imports from _sample.pyd.
Right click on the project, and select Properties, Configuration Properties, Linker, Input. In Additional Dependencies enter:
```
"$(PYTHON_LIB)"
```

Usage

>python
>>> import sample
>>> c = sample.Client()
>>> c.setName("Patrick")
>>> c.getName()
'Patrick'
>>> m = sample.Matter()
>>> m.setNumber(12)
>>> m.setDescription('Purchase: 4 Lower Meadow')
>>> m.getNumber()
12
>>> m.getDescription()
'Purchase: 4 Lower Meadow'
>>>

Sample

This sample is a modified version of the class example (copied from the SWIG install folder, Examples/python/class):

Create a command prompt with the environment set-up correctly (see above).
Checkout the project from Subversion:

https://weezy/svn/learn/python/swig/example-class
From the command prompt, open the project in Visual Studio 2005:
```
"C:\Program Files\Microsoft Visual Studio 8\Common7\IDE\devenv.exe" example.vcproj
```
Note: The example_wrap.cxx source file is generated by swig.exe.
Switch the project to Release configuration (the standard python install does not include the debug version of the python libraries).
Build the project.

Note: The Custom Build Step can be viewed from within the IDE, by right clicking on example.i, selecting Properties followed by Custom Build Step, then selecting the ... option from the Command Line property (alternatively open example.vcproj using a text editor).
Run the python script… see the Usage section above.

Issues

AttributeError

If you get an error like this…

>>> c.getMatters()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "sample.py", line 55, in <lambda>
    __getattr__ = lambda self, name: _swig_getattr(self, Client, name)
  File "sample.py", line 34, in _swig_getattr
    raise AttributeError,name
AttributeError: getMatters

…then try a project Rebuild…

You can see if the method is defined by searching for the SwigMethods array in the generated _wrap.cxx file (e.g. sample_wrap.cxx).