Hi,
I'm new to Python's C API and developing my very first project using
Boost::Python (bpy). My goal is executing user defined scripts within an
embedded python environment using custom stdout and stderr and providing
a special built in module.
Beside a bunch of classes (which can be defined using bpy quite
comfortable) the module shall contain a couple of functions
and since bpy is apparently not primarily targeted at embedding and
doesn't provide a function type this is the point where all my problems
start.
My current solution is to get the global scope:
global = import("__main__").attr("__dict__");
And add my module using Py_InitModule3:
global["my_mod"] = object(handle<>(borrowed(Py_InitModule3("my_mod",
functions, "docstr"))));
Adding classes and there methods is a nice, clear and easy task:
global["my_mod"].attr("__dict__")["myclass"] =
class_<CPPClass, boost::noncopyable>("myclass", bpy::init<>())
.def("f1", &CPPClass::f1)
.def("f2", &CPPClass::f2);
But the functions need to be in the functions parameter of
Py_InitModule3, defined like:
PyMethodDef functions[] = {
{"f1", &f1, METH_VARARGS, "my_doc"},
{"f2", &f2, METH_VARARGS, "my_doc"},
{0, 0}
};
And now the implementations have to be PyCFunction type, i. e. have the
signature PyObject* (PyObject*, PyObject*), not a (more or less)
arbitrary one they could have when used in bpy's def(). This means the
number of arguments given to the function within the python code could
be wrong, I need to convert from PyObject to bpy types to C++ types and
all the way back and there are traps like returning temporary pointers
or memory leaks.
An implementation could look like:
PyObject* f1(PyObject* self, PyObject* args)
{
bpy::handle<> arg1, arg2;
PyArg_UnpackTuple(args, "func", 1, 2, &arg1, &arg2);
if (arg2.get()) {
...
}
...
...bpy::extract<const char*>(bpy::object(arg1))...
return Py_BuildValue("s", my_cstr_result);
}
Beside the problems already mentioned this means missing bpy features
for the functions like automatic docstrings, return value policies etc.
So I would really like to know whether there's a better way to do what
I'm doing. Especially a more boost like way ;-)
Thanks for any reply!
Christopher Schramm
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