CRFsuite Python module via SWIG

* HOW TO BUILD

0. Build CRFsuite and install it (the library and include files are necessary)

1. Generate a SWIG wrapper
$ ./prepare.sh

2. Build the binding.
$ python setup.py build_ext

3. Install the binding.
$ python setup.py install

4. Run the binding.
$ python
Python 2.6.6 (r266:84292, Sep 15 2010, 16:22:56)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import crfsuite
>>>


* SAMPLE PROGRAMS
Refer to sample_train.py and sample_test.py



* NOTES FOR INSTALLING CRFSUITE IN A NON-DEFAULT DIRECTORY

If you have changed the installation directory of CRFsuite using --prefix
option for the configure script, please specify the include and library
directories to setup.py; for example, if you have installed CRFsuite into
$HOME/local directory, run:

$ python setup.py build_ext --include-dir=$HOME/local/include --library-dirs=$HOME/local/lib -R $HOME/local/lib

If you forget to specify "-R PATH_TO_CRFSUITE_LIBRARY" to the arguments,
you may get this kind of error:

$ python
Python 2.6.6 (r266:84292, Sep 15 2010, 16:22:56)
[GCC 4.4.5] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import crfsuite
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "crfsuite.py", line 25, in <module>
    _crfsuite = swig_import_helper()
  File "crfsuite.py", line 21, in swig_import_helper
    _mod = imp.load_module('_crfsuite', fp, pathname, description)
ImportError: libcrfsuite-0.12.so: cannot open shared object file: No such
file or directory

This error reports that CRFsuite Python module could not resolve the reference
to the CRFsuite library (libcrfsuite-0.12.so). If you encounter this problem,
please rebuild the Python module with "-R PATH_TO_CRFSUITE_LIBRARY".
Alternatively, you can specify a search path for libraries:

$ export LD_LIBRARY_PATH=$HOME/local/lib



* NOTES FOR TESTING THE PYTHON MODULE WITHOUT INSTALLING IT

Adding "--inplace" option to the command-line argument of setup.py builds
_crfsuite.so in the current directory. If these files are placed on the
directory included in the module path of Python (e.g., the current directory
where a Python process is created), one can try the module without running
"python setup.py install"

$ python setup.py build_ext --inplace



* NOTES FOR GENERATING WRAPPER CODE USING SWIG.

The script "prepare.sh" can generate a SWIG wrapper with "--swig" option.
$ ./prepare.sh --swig

However, we may get a compiling error for the wrapper code (export_wrap.cpp)
even with the latest version of SWIG (2.0.4):

export_wrap.cpp:5019: error: redefinition of ?struct swig::traits<std::vector<
CRFSuite::Attribute, std::allocator<CRFSuite::Attribute> > >
export_wrap.cpp:4918: error: previous definition of ?struct swig::traits<std::
vector<CRFSuite::Attribute, std::allocator<CRFSuite::Attribute> > >
error: command 'g++' failed with exit status 1

Having no idea how to fix this problem elegantly, I simply remove the latter
definition from export_wrap.cpp manually. This is why I end up including
the wrapper code into the source repository.