[C++-sig] Embedding...

[Beau Sapach]

Thanks again for your help Stefan!

I'm trying to compile a simple example based on your code but I'm getting
link errors, unresolved externals for both exec and import functions.  Does
this mean that they are not built into my boost_python.lib?  I've downloaded
and built the CVS version using the visual studio .dsw file.  Now I'm
guessing it's not up to date?

Beau

-----Original Message-----
From: c++-sig-bounces at python.org [mailto:c++-sig-bounces at python.org] On
Behalf Of Stefan Seefeld
Sent: Wednesday, October 25, 2006 11:46 AM
To: Development of Python/C++ integration
Subject: Re: [C++-sig] Embedding...

Beau Sapach wrote:
> Hello everyone,
> 
> Thanks Stefan for your help! I know I'm posting a lot to this list, 
> but I must admit I'm having a hard time wrapping my head around
boost.python.
> 
> If I want to make an instance of an object in C++ available to a 
> python interpreter within the same .exe I must first expose the class
correct?
> Using the same method described in the tutorial?

Right.

> Once that's done could I expose a global function (again within the 
> same
> exe) that would return a pointer to an instance of the previously 
> exposed class?  Or is there an easier way of simply passing this to
python?

Assuming you have set up a module 'world', containing a class 'hello'
(exported via the aforementioned class_<> harness), you can instantiate an
object of that type as:

----C++ code----
namespace bpl = boost::python;
bpl::object main = python::import("__main__"); bpl::object
global(main.attr("__dict__")); // Load the 'hello' module.
bpl::object result = bpl::exec("import hello\n", global, global); // Get
hold of the hello.world class.
bpl::object hello_class = global["hello.world"]; // Instantiate it.
bpl::object hello_instance = hello_class(); // Inject it into environment.
global['hello_instance'] = hello_instance; // And run a script with it.
result = bpl::exec_file(script_name, global, global); // Recover things from
environment.
bpl::object greeting = global["greeting"];
----------------


The script itself can now assume the existence of 'hello_instance', which
was placed into the environment just before the script was invoked with it
(see above):

----python code----
# let's assume the 'hello.world' class exposes a 'greet' method.
greeting = hello_instance.greet()
-------------------

'greeting' becomes a new variable in the environment, which can be extracted
after the script's execution has finished. (See above.)


As you can see, the main device to exchange data between the C++ runtime and
the environment seen by the script is the 'global' dictionary that gets
passed to the exec / exec_file calls. It works two-ways.


HTH,
		Stefan

-- 

      ...ich hab' noch einen Koffer in Berlin...
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