Thanks for everyone's help. I'm posting my updated class that is now working.
class Scene : public boost::enable_shared_from_this
{
public:
void sendYourselfToPython()
{
try {
object ignored = exec(EXAMPLE_PY_FUNCTION, pyMainNamespace);
object processFileFunc = pyMainModule.attr("Foo").attr("processFile");
processFileFunc(shared_from_this(), "test.txt");
} catch (boost::python::error_already_set const &) {
std::string perror = parse_python_exception();
std::cerr << "Error in Python: " << perror << std::endl;
}
}
};
typedef boost::shared_ptr SceneP;
On Fri, Sep 2, 2011 at 9:08 PM, Dave Abrahams wrote:
>
> on Fri Sep 02 2011, Josh Stratton wrote:
>
>> Here's a really short example of what I don't understand. Basically I
>> can setup the python function to accept shared pointers, but can I
>> setup it to also use normal pointers?
>
> Yes, once you've exposed the class to Python, you can pass pointers to
> Python. However, Boost.Python won't let you pass raw pointers around
> without telling it (via call policies) what you want to do about
> lifetime management... actually what it will do, if you don't tell it
> otherwise, is copy the pointee, which is at least safe from an object
> lifetime point-of-view.
>
>> In the example code attached, if I uncomment
>> scene->sendYourselfToPython(); it fails because it's using "this" as
>> the scene pointer.
>
> (It's already uncommented)
>
>> Error in Python: : No to_python
>> (by-value) converter found for C++ type: Scene
>
> ...because you've said it's noncopyable, there's no way to copy the
> pointee, which is what happens when it is passed by value.
>
>> So it appears to only work for shared pointers at this point. Can I
>> also get it to work with "this" at the same time? Jim pointed me to
>> "enable_shared_from_this" as a way for creating a shared pointer
>> object, which makes sense from the docs of how to do it, but I was
>> wondering if I necessarily NEED to send it down as a shared pointer.
>
> There *are* things you can do to subvert Python's checking, but they're
> highly discouraged. Jim is on the right track: if you want to pass a
> mutable reference to the object and you want its lifetime to be properly
> managed, you should do what he's saying. If you don't like
> using enable_shared_from_this, of course, you can just do it outside a
> member function:
>
> void sendSceneToPython(SceneP s)
> try {
> object ignored = exec(EXAMPLE_PY_FUNCTION, pyMainNamespace);
> object processFileFunc = pyMainModule.attr("Foo").attr("processFile");
> processFileFunc(s, "test.txt");
> } catch (boost::python::error_already_set const &) {
> std::string perror = parse_python_exception();
> std::cerr << "Error in Python: " << perror << std::endl;
> }
> }
>
> HTH,
>
> --
> Dave Abrahams
> BoostPro Computing
> http://www.boostpro.com
>
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