building boost python examples using Visual Studio 2008

Question

I'm using Boost Python library to create python extensions to my C++ code. I'd like to be able to invoke from python the 'greet' function from the C++ code shown below:

#include <boost/python/module.hpp>
#include <boost/python/def.hpp>

char const* greet()
{
   return "hello, world";
}

BOOST_PYTHON_MODULE(hello_ext)
{
    using namespace boost::python;
    def("greet", greet);
}

And the python code :

import hello_ext
print hello_ext.greet() 

I've managed to do this using the bjam (hello_ext.pyd is generated and it works nice), but now I'd like to build it using Visual Studio 2008. A hello.dll gets built (but neither hello_ext.dll nor any .pyd). After invoking my python code I get an error:

ImportError: No module named hello_ext.

After renaming the hello.dll to hello.pyd or hello_ext.pyd, I get another ImportError: Dll load failed

How can I build the correct .pyd file using VS 2008?

Answer 1

Firstly, make sure you only try to import the release version from Python; importing the debug version will fail because the runtime library versions don't match. I also change my project properties so that the release version outputs a .pyd file:

Properties >> Linker >> Output:

$(OutDir)\$(ProjectName).pyd

(I also create a post-build action to run unit tests from python)

Next, make sure you define the following in your stdafx.h file:

#define BOOST_PYTHON_STATIC_LIB

Lastly, if you have more than one python version installed, make sure that you're importing the right version of python.h (in Tools >> Options >> Projects and Solutions >> VC++ Directories >> Include Files).

Answer 2

The error ImportError: Dll load failed usually means that your .pyd module depends on other DLLs that couldn't be found - often msvc*.dll. You may want to try opening the .pyd file in Notepad and searching for ".dll". Then check if all of the DLL dependencies exist in your directory or PATH.

Or use Dependency Walker which will find missing dependencies for you