[C++-sig] Calling python function from C++
dave at boost-consulting.com
Wed Nov 13 04:08:43 CET 2002
"Bjorn Pettersen" <BPettersen at NAREX.com> writes:
> In http://www.boost.org/libs/python/doc/v2/callbacks.html it says
> "...given an _object_ instance f holding the function...", however I
> can't find a simple way to get a reference to a Python function into
> an object instance.
> My test code is:
> "def hello(s): \n"
> " return 'hello ' + s \n",
> Py_file_input, ns, ns);
The PyRun_String docs say:
PyObject* PyRun_String(char *str, int start, PyObject *globals, PyObject *locals)
Return value: New reference.
Which means you're leaking a reference here.
> PyObject* fn = PyRun_String("hello", Py_eval_input, ns, ns);
> I then want code with the same semantics as:
> PyObject* res = PyObject_CallFunction(fn, "s", "world");
> std::string cpp_res = PyString_AsString(res);
> the closest I've gotten is:
> object hello = object(handle<>(borrowed(fn)));
Why are you using borrowed()? That causes another reference to be
> object res = hello("world");
> std::string cpp_res = extract<std::string>(res);
> I found the wrapping of 'fn' in the example in the "errors.hpp"
> section. Is this the easiest/correct way to do this?
You want something like:
handle<> fn = PyRun_String("hello", Py_eval_input, ns, ns);
std::string cpp_res = extract<std::string>(hello("world"));
> question: are the reference counts in the Boost example all taken
> care of at end-of-scope?
dave at boost-consulting.com * http://www.boost-consulting.com
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