Lttoolbox API
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You can use lttoolbox as a library in C++ by with #include <lttoolbox/fst_processor.h>, and with a bit more work, you can also use it from Python.
Using as a library in C++
For this example you will need two files, test.dix:
<dictionary>
<alphabet/>
<sdefs>
<sdef n="n"/>
<sdef n="pl"/>
</sdefs>
<section id="main" type="standard">
<e><p><l>cars</l><r>car<s n="n"/><s n="pl"/></r></p></e>
</section>
</dictionary>
And test.cc:
#include <stdio.h>
#include <string>
#include <iostream>
#include <lttoolbox/fst_processor.h>
#include <lttoolbox/ltstr.h>
using namespace std;
FSTProcessor fstp;
int main(int argc, char **argv)
{
if(argc < 2) {
wcout << L"Please specify a transducer" << endl;
exit(-1);
}
FILE *t_rl = fopen(argv[1], "r");
fstp.load(t_rl);
fclose(t_rl);
fstp.initBiltrans();
wstring input = L"^car<n><pl>$";
wstring trad = fstp.biltrans(input);
wcout << input << L" --> " << trad << endl;
return 0;
}
Compile both of the files:
$ lt-comp rl test.dix test_rl.bin main@standard 6 5 $ g++ -Wall test.cc -o test -llttoolbox3
And then test:
$ ./test test_rl.bin ^car<n><pl>$ --> ^cars$
Using as a module from Python
This example is based on how libvoikko uses lttoolbox for analysis. We make a C++ library that exposes whatever lttoolbox functions we need to Python, and a little Python class that makes calling those functions a bit more pythonic.[1]
Write the following files:
libltpy.h:
#include <lttoolbox/fst_processor.h>
class Analyser {
public:
Analyser(const std::string & directoryName) throw(exception);
wstring analyse(wstring const &word);
private:
FSTProcessor fst;
};
libltpy.cc:
#include "libltpy.hpp"
#include <lttoolbox/fst_processor.h>
using namespace std;
Analyser::Analyser(const string & analyserpath) throw(exception) {
FILE * file = fopen(analyserpath.c_str(), "r");
if (!file) {
cerr << "Couldn't open analyser file " << analyserpath << endl;
throw exception();
}
fst.load(file);
fclose(file);
fst.setCaseSensitiveMode(false);
fst.setDictionaryCaseMode(true);
fst.initBiltrans();
}
wstring Analyser::analyse(wstring const &word) {
pair <wstring,int> analysis = fst.biltransWithQueue(word, false);
// or fst.biltrans, which just returns the string. The 'false'
// means no ^ or $ in input/output
if (analysis.second == 0) {
return analysis.first;
}
else {
// a partial match:
return L"@"+analysis.first;
}
}
extern "C" wstring * analyse(Analyser * a, const wchar_t * word) {
// TODO: there must be a way to just send in a wstring in the first p
size_t wlen = wcslen(word);
wstring inputString = L"";
for (size_t i = 0; i < wlen; i++) {
inputString.append(1, word[i]);
}
wstring * out = new wstring(a->analyse(inputString));
return out;
}
extern "C" Analyser * init(const char ** error, const char * path) {
Analyser * a = 0;
try {
a = new Analyser(path);
}
catch (exception & e) {
delete a;
a = 0;
*error = e.what();
return 0;
}
*error = 0;
return a;
}
extern "C" void terminate(Analyser * a) {
delete a;
}
lt.py:
# -*- coding: utf-8 -*-
from ctypes import byref, CDLL, c_char_p, c_wchar_p, c_void_p, POINTER
class FST(object):
def __init__(self, libpath, fstpath):
self.__lib = CDLL(libpath)
self.__lib.init.argtypes = [POINTER(c_char_p), c_char_p]
self.__lib.init.restype = c_void_p
self.__lib.terminate.argtypes = [c_void_p]
self.__lib.terminate.restype = None
self.__lib.analyse.argtypes = [c_void_p, c_wchar_p]
self.__lib.analyse.restype = POINTER(c_wchar_p)
error = c_char_p()
self.__handle = self.__lib.init(byref(error), fstpath)
if error.value != None:
self.__handle = 0
raise Exception(u"Initialization of fst failed: " + unicode(error.value, "UTF-8"))
def __del__(self):
if (self.__handle != 0):
self.__handle = 0
class DummyLib:
def __getattr__(obj, name):
raise Exception("Attempt to use library after terminate() was called")
self.__lib = DummyLib()
def analyse(self, word):
analyses = self.__lib.analyse(self.__handle, word)
return analyses.contents.value
Compile the C++ files so you get a file like libltpy.so. The following commands worked for me:
g++ -DGCC_VISIBILITY=1 -g -O2 -fvisibility=hidden -I/usr/local/include/lttoolbox-3.2 -I/usr/local/lib/lttoolbox-3.2/include -c libltpy.cpp -fPIC -DPIC -o libltpy.o g++ -fPIC -DPIC -shared libltpy.o -Wl,-rpath -Wl,/usr/local/lib -Wl,-rpath -Wl,/usr/local/lib -L/usr/local/lib /usr/local/lib/liblttoolbox3.so -Wl,-soname -Wl,libltpy.so.0 -o libltpy.so
However, if you use autotools, you typically just need the following in your Makefile.am:
lib_LTLIBRARIES = libltpy.la libltpy_la_SOURCES = libltpy.cpp libltpy_la_LDFLAGS = $(LTTOOLBOX_LIBS)
then autogen.sh and make libltpy.la (see #Real-world examples).
Then use it like:
import lt
fst = lt.FST("libltpy.so", "analyser.bin")
print fst.analyse(u"cars") # should print car<n><pl>
Real-world examples
- apertium-transfer uses lttoolbox from C++ to look up words in the bidix
- libvoikko uses lttoolbox from C++ to analyse words, and also makes a Python module:
Footnotes
- ↑ An alternative might be to include Python.h in the C++ code, and define a full Python class from there, like how pylibtextcat/py3libtextcat creates a Python class for a C library.
