Well what I really to do is turn an STL vector into and python list. I want
to do this in a separate script, so I don't think eval is right for me. I
just started with an int because that's easier. I've gotten that part too,
my code looks like this:
int main(){
int
five_squared=0;
int a =3;
try {
Py_Initialize();
object main_module = import("__main__");
object main_namespace = main_module.attr("__dict__");
main_namespace["var"]=a;
object ignored = exec("result = 5 ** var", main_namespace);
five_squared = extract(main_namespace["result"]);
} catch( error_already_set ) {
PyErr_Print();
}
std::cout << five_squared << std::endl;
return 0;
}
This code works just like you expect it to, it prints 5^3 or 125.
However I try to change my code to this
int main(){
int
five_squared=0;
std::vector v(2);
v[0]=2;
v[1]=3;
try {
Py_Initialize();
object main_module = import("__main__");
object main_namespace = main_module.attr("__dict__");
main_namespace["var"]=v;
object ignored = exec("result = 5 ** var[1]",
main_namespace);
five_squared = extract(main_namespace["result"]);
} catch( error_already_set ) {
PyErr_Print();
}
std::cout << five_squared << std::endl;
return 0;
}
I want this to print 5^2 or 25. But instead I get this error:
TypeError: No to_python (by-value) converter found for C++ type:
std::vector >
Which makes sense, python doesn't know how to handle stdd::vector. So I
have to make something to do this conversion. This is where I'm stuck now,
I think I have to do something like this
BOOST_PYTHON_MODULE(vector_indexing_suite_ext){
boost::python::class_ >("PyVec")
.def(boost::python::vector_indexing_suite >());
}
Is this all I need? Do I need to define __getitem__ ? If this is all I
need how do I use it in main()?
Also does anyone know of any good resources for embedding in boost.python?
Thanks!
On Sat, Jan 9, 2010 at 2:55 PM, Stefan Seefeld wrote:
> On 01/09/2010 01:52 PM, devin kelly wrote:
>
>> Hello,
>>
>> I'm trying to expose some data that I develop in C++ to python.
>> Basically, the reverse of this sample code:
>>
>> #include
>> #include
>> #include
>> #include
>>
>> int main(){
>>
>>Py_Initialize();
>>object main_module = import("__main__");
>>object main_namespace = main_module.attr("__dict__");
>>ignored = exec("result = 5 ** 2", main_namespace);
>>int five_squared = extract(main_namespace["result"]);
>>std::cout << five_squared << std::endl;
>>
>>return 0;
>> }
>>
>>
>> So this code starts the python interpreter, squares 5 (in python) and then
>> extracts the result to an int called five_squared. This works fine for me,
>> it's basically an example straight out of the boost.python webpage.
>>
>> What I'd really like to do though is have an int that I initialize in C++
>> and then square in python. So this would require me to pass (or expose)
>> that data to python. I've been trying this for a while and have had no luck
>> whatsoever. The best I can think of is code like this:
>>
>> int main(){
>>Py_Initialize();
>>object main_module = import("__main__");
>>object main_namespace = main_module.attr("__dict__");
>>main_namespace["num2square"] = 6;
>>ignored = exec("result = num2square ** 2", main_namespace);
>>int five_squared = extract(main_namespace["result"]);
>>std::cout << five_squared << std::endl;
>>return 0;
>> }
>>
>> This doesn't work. Python throws an error. What am I doing wrong??
>>
>
> It might help indicating what error Python actually throws.
>
> Also, if all you want is to evaluate an expression, I'd suggest you use
> "eval()", not "exec()".
>
>Stefan
>
> --
>
> ...ich hab' noch einen Koffer in Berlin...
>
>
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