On Sat, Apr 16, 2011 at 9:46 AM, Roger House <rho...@sonic.net> wrote:
> I'm a Python newbie who's been given a task requiring calls of Python code
> from a C++ program. I've tried various tutorials and dug into The Python/C
> API doc and the Extending and Embedding Python doc, but I haven't been able
> to answer this question:
>
> Is it possible in a C++ program to generate Python code, execute
> it, and get output back (say a tuple of 10 or so items) without
> doing any file i/o?
>
> Clearly it works to write the generated Python to a file and then use
> PyImport_Import and PyObject_CallObject to call a function returning the
> output tuple. But it seems like it should be possible to do this without
> writing the Python code to a file. I tried PyRun_String, but I can't see
> how it
> can be used to return a tuple (the Py_file_input option always returns
> None).
What I do for this is have the Python code place its return value into
a particular location. If you're using file input, I think it's
restricted to returning an integer; but you can do something like
this:
const char *python_code="result=('hello','world',42)";
PyObject *globals=... (use same as locals if you don't need globals)
PyObject *locals=PyDict_New();
Py_XDECREF(PyRun_StringFlags(python_code,Py_file_input,globals,locals,0);
PyObject *returned_tuple=PyDict_GetItemString(locals,"result");
Py_DECREF(locals);
You now own a reference to whatever the Python code put into its
variable "result", in the C variable returned_tuple. Of course, it
might not be a tuple at all, and it might not even be present (in
which case returned_tuple will be NULL). This is a fairly effective
way for Python to return hefty amounts of data to C.
Don't forget to decref the return value.
Hope that helps!
Chris Angelico
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