How do I import modules in boost::python embedded python code?

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

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.