How do I import modules in boost::python embedded

Question

I'm using boost::python to embed some python code into an app. I was able to get print statements or other expressions to be evaluated properly, but when I try to import modules, it is not importing and application is exiting. Further the globals() function call in the embedded code gives a runtime error too.

#include <boost/python.hpp>

using namespace boost;
using namespace boost::python;
using namespace boost::python::api;

int main(void) {
    Py_Initialize();
    object main_module = import("__main__");
    object main_namespace = main_module.attr("__dict__");
    main_namespace["urllib2"] = import("urllib2");

    object ignored = exec(
            "print 'time'\n", main_namespace);
}

Here, I've tried to import urllib2 using the boost import function, this compiles and runs properly, but with the following exec statement, it gives an error.

    object ignored = exec(
            "print urllib2\n"
            "print 'time'\n", main_namespace);

Or when I remove the boost import function and do the import from within the embedded code also, it gives an error. I tried using a try: except: block but that doesn't work either. Is this because the C++ app isn't able to find the location of the urllib2 py module or something? Is there a way to set the path of the module before trying to import?

This is being built only for internal use, so some hard coding of the paths is acceptable.

Edit: More info:
This is what happens. I did a try .. catch and called the PyErr_Print() when ever there is an exception, and got this as error all the time when there are module imports or even function calls. Error message:

Traceback (most recent call last):
  File "<string>", line 1, in <module>
TypeError: 'NoneType' object does not support item assignment

Can anyone think of any reason?

Answer 1

If you haven't already, you need to

import sys
sys.path.append("/home/user/whatever")

That took care of my problems a couple of years ago when embedding boost::python (Python v2.5).

Edit:

Poked around in old code. Perhaps this does the trick:

Py_SetProgramName(argv[0]);
Py_InitializeEx(0);

Sounds unsure that you should really need the Py_SetProgramName(), but I faintly remember some fishy business there.

Answer 2

I ran into the same problem as you, i e a very simple example resulting in the TypeError, and found the answer in this question, which was to supply the namespace twice, both as global and local.

Answer 3

That didn't help, but I found a different solution to my problem. My current code looks like this:

#include <boost/python.hpp>
#include <iostream>

using namespace std;
using namespace boost;
using namespace boost::python;
using namespace boost::python::api;

int main(void) {
        Py_Initialize();
        boost::python::object http = boost::python::import("urllib2");

        try
        {
                boost::python::object response = http.attr("urlopen")("http://www.google.com");
                boost::python::object read = response.attr("read")();
                std::string strResponse = boost::python::extract<string>(read);
                cout << strResponse << endl;
        }
        catch(...)
        {
                PyErr_Print();
                PyErr_Clear();
        }
}

Anyways, thanks for the answer Jonas