On 01/21/2014 01:52 PM, Gary Oberbrunner wrote:
>
> ----- Original Message -----
>> From: "Stefan Seefeld" <ste...@seefeld.name>
> ...
>> It seems what you really want is a way for your C++ code to
>> manipulate pure Python objects, without any automatic type conversion.
> Yes!
>
>> So the cleanest way to do that would be to use the above definition of
>> the "Effect" class (in Python), import that into your C++ runtime
>> (via bpl::import()), and then instantiate an "Effect" object with your
>> pre-defined dict object.
> I'm trying to do this in a boost python extension, so it has to be all in
> C++. If I have to wrap some python around it, it'll become a bit too
> heavyweight.
Have a look at the attached code; I don't think that counts as
heavy-weight. In particular, trying to do the same without embedding a
little "script" would be just more cumbersome, if it worked at all.
> I'd love to do what you suggest above, if it can be done all in C++. I think
> all I need is a way to create, in C++, an empty Python class object with a
> __dict__. Then, as you say, I can add attributes to it (at least I think I
> should be able to - but I'm not sure how far the boost.python world goes).
Compile the attached as a stand-alone app. I think it demonstrates what
you want, so you should be able to easily adjust it to your use-case.
Stefan
--
...ich hab' noch einen Koffer in Berlin...
#include <boost/python.hpp>
#include <string>
namespace bpl = boost::python;
char const *code =
"class Struct: \n"
" def __init__(self, attrs): \n"
" self.__dict__.update(attrs) \n";
int main(int argc, char** argv)
{
Py_Initialize();
try
{
// set up a tiny Python session to define a "Struct" class.
bpl::object main = bpl::import("__main__");
bpl::object global(main.attr("__dict__"));
bpl::object result = bpl::exec(code, global, global);
bpl::object type = global["Struct"];
// now instantiate it with a dictionary.
bpl::dict attrs;
attrs["number"] = 42;
bpl::object o = type(attrs);
// and show that it contains the expected attribute(s)
std::cout << bpl::extract<char const *>(bpl::str(o.attr("number"))) << std::endl;
}
catch (bpl::error_already_set &)
{
PyErr_Print();
}
}
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