Boost not exposing module to python

Question

I'm using some example code I found on the web to try to set up libboost so I can call into cpp routines with Python code. (I intend to use python to write my UI and cpp for my backend for this application) Boost seems simple enough to use, but it's currently not exposing any functionality.

#include <boost/python.hpp>

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

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

I compile this using the line g++ -c hello.cpp -I/usr/include/python3.6/ (that last include is necessary because I'm on ubuntu, where g++ doesn't locate python correctly, and I'm too lazy to add it to my path)

import hello_ext
print(hello_ext.greet())

I run this using python3, and I get the following output

  File "hello.py", line 1, in <module>
    import hello_ext
ModuleNotFoundError: No module named 'hello_ext'

This implies to me that Boost is not properly exposing the C++ functionality I created a module for. What am I missing here? I've already tried exposing the functionality to python in a header file instead of in the cpp file, and that has the same result.

Also, if anyone looking at this post is having issues accessing functionality within their module, but it seems like the module is being exposed, make sure python doesn't already have a default module with the same name which would take precedence over your module.

Answer 1

According to boost::python docs your code should be compiled as a shared library to be used in python:

g++ hello.cpp -I /usr/include/python3.6 -lboost_python-py36 -shared -fPIC -o hello_ext.so

Note that the name of the shared library must be the same as the name of your python module. You also forgot to link your code with boost lib.