Running c++ code from python using Boost.Python

I am currently reading a book "Production Volume Rendering". The book images were the main reason I started reading it. However, since the content of the book is written into a library"PVR" which is written in C++ but it is controlled using Python scripts. Thus, to get started, I needed to understand how the whole thing is chained from the c++ code to the python scripts. So I started to get my c++ code to work from a Python script so here it is. This is what I learned. I used VisualStudio 2010 and python27.

In visualstudio 2010, create a new empty win32 dll project named "hello". Next create an empty c++ file. The contents of the file are as follows:

#include < iostream >
using namespace std; 
void say_hello(const char* name) { 
   cout << "Hello " <<  name << "\n"; 
} 

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

using namespace boost::python; 

BOOST_PYTHON_MODULE(hello) { 
   def("say_hello", say_hello); 
} 

Nothing fancy here. I simply create a function that says hello world on screen usign standard IO routine. 

In order to have my function exported properly I added a module definition file (.def) to the project. This file contains: 
LIBRARY hello 
EXPORTS say_hello 

This tells the compiler to add the say_hello function to dll. 
Next, I compiled and build the dll if all goes well you have the dll created.

Now on the python side. I copied my hello.dll file to an empty directory. This directory contained another file i.e. my python script (hello.py). The python script contains:
import hello 
hello.say_hello("World")

I tried to run the python script using python hello.py 
This returned the following error 
d:\TestHello > python hello.py 
Traceback (most recent call last): 
File "hello.py", line 1, in import hello 
ImportError: No module named hello 

Now searching online I found that for my dll to be recognized by Python, it needs to be renamed to .pyd extension. So i changed the extension to .pyd and ran the python script again. This time, it gave me another error which was 
d:\TestHello > python hello.py 
Traceback (most recent call last): File "hello.py", line 1, in import hello 
ImportError: DLL load failed: The specified module could not be found. 

Now once again I went online to find the reason for this error. Fortunately, on one of the websites, I found the reason for this error. Basically, the Python interpreter is unable to load a dependency dll while loading my hello.pyd (dll). Which dll is it? This I came to know by opening my hello.pyd(dll) in the dependency walker (http://www.dependencywalker.com/). This showed me that I was missing the boost_python-vc100-mt-gd-1_51.dll which is needed. So i copied this dll to the same place as my hello.pyd (dll). 

Now running the python script again ran the code fine. 
d:\TestHello > python hello.py 
Hello World! 

Some notes to take away: 
1) Rename your c++ dll to .pyd otherwise Python will not load it. 
2) Name the module name the same as your dll name i.e. BOOST_PYTHON_MODULE(< your dll name >) 
3) Make sure that all of the dependency dlls are in the same folder or in the path. 

Hope this helps others. I went through a lot of pain with this one. But finally I got it working.