C++ Boost.Python : 2 problems - c++

Question

So, i search good tool to integrate my C++ code with python, and at first i looked at boost.python.
I've get hello examle from boost documentation and try to build and run it. Source code is (src/hello.cpp):
#include <Python.h>
#include <boost/python.hpp>
char const* greet()
{
return "hello, world";
}
BOOST_PYTHON_MODULE(hello_ext)
{
using namespace boost::python;
def("greet", greet);
}
Problem 1 - Windows and mingw
I try to build and my result :
g++ -o build\hello.o -c -IE:\Programming\libs\boost_1_48_0 -IE:\Programming\Python\include src\hello.cpp
g++ -shared -o pyhello.dll build\hello.o -LE:\Programming\libs\boost_1_48_0\stage\lib -LE:\Programming\Python\libs -lboost_python-mgw45-mt-1_48 -lpython27 -Wl,--out-implib,libpyhello.a
Creating library file: libpyhello.a
build\hello.o:hello.cpp:(.text+0x20): undefined reference to `_imp___ZN5boost6python6detail11init_moduleEPKcPFvvE'
Also similar 4 undefined errors with boost::python.
My build boost command line : bjam toolset=gcc variant=release
I found similar troubles in google (and on stackoverflow too), but didn't found answer at my case.
Problem 2 - Using module (linux)
At linux platform i've no problem with building module, same source compiled well :
g++ -o build/hello.os -c -fPIC -I/usr/include/python2.7 src/hello.cpp
g++ -o libpyhello.so -shared build/hello.os -lboost_python -lpython2.7
Now, how can i use that? In documentation no words about module naming, quote :
can be exposed to Python by writing a Boost.Python wrapper:
#include <boost/python.hpp>
BOOST_PYTHON_MODULE(hello_ext)
{
using namespace boost::python;
def("greet", greet);
}
That's it. We're done. We can now build this as a shared library. The
resulting DLL is now visible to Python. Here's a sample Python
session:
>>> import hello_ext
>>> print hello_ext.greet()
hello, world
So, my module named: libpyhello.so, but how i can use it in python iterpreter? I try import pyhello, hello_ext, libpyhello - and only with libpyhello interpreter is printed :
ImportError: dynamic module does not define init function (initlibpyhello)
All other variants of import failed with : ImportError: No module named pyhello
UPDATE 2nd question : Solved, *.so module must be named as ID used in BOOST_PYTHON_MODULE. After i change : BOOST_PYTHON_MODULE(hello_ext) to BOOST_PYTHON_MODULE(libpyhello), module is imported well as libpyhello.

Answer 1

It's important that the library file is named like you declare the module here:
BOOST_PYTHON_MODULE(hello_ext)
that is hello_ext.dll or hello_ext.so.

Answer 2

Hi，I have got the same problem as yours under win7 32bit with mingw， however I fixed it at last.
The possible solution is：
When build the lib boost python, use link=shared instead.
like:
bjam stage toolset=gcc --with-python link=shared threading=multi runtime-link=shared variant=release,debug --user-config=user-config.jam cxxflags="-include cmath "
When link，use the BOOST_PYTHON_STATIC_LIB macro explicitly
The following is the sample cmd line：
g++ hello_ext.cpp -shared -O3 -DBOOST_PYTHON_STATIC_LIB -lboost_python -lpython25 -o hello_ext.pyd
To save your time，just add some lines in file boost\python.hpp：
#include <cmath> //fix cmath:1096:11: error: '::hypot' has not been declared
#if defined(__MINGW32__) && defined(_WIN32)
#if !defined(BOOST_PYTHON_SOURCE)
#define BOOST_PYTHON_STATIC_LIB
#endif
#endif
... here,other includes files ...
Then, you can simply use cmd like this:
g++ hello_ext.cpp -shared -lboost_python -lpython25 -o hello_ext.pyd
This shell will be ok, have a try.