I am essentially trying to write a console interface with input and output for an embedded python script. Following the instructions here, I was able to capture stdout:
Py_Initialize();
PyRun_SimpleString("\
class StdoutCatcher:\n\
def __init__(self):\n\
self.data = ''\n\
def write(self, stuff):\n\
self.data = self.data + stuff\n\
import sys\n\
sys.stdout = StdoutCatcher()");
PyRun_SimpleString("some script");
PyObject *sysmodule;
PyObject *pystdout;
PyObject *pystdoutdata;
char *string;
sysmodule = PyImport_ImportModule("sys");
pystdout = PyObject_GetAttrString(sysmodule, "stdout");
pystdoutdata = PyObject_GetAttrString(pystdout, "data");
stdoutstring = PyString_AsString(pystdoutdata);
Py_Finalize();
The problem with this is that I only recieve the stdout after the script has finished running, whereas ideally for a console the stdoutstring would update as the python script updates it. Is there a way to do this?
Also, how would I go about capturing stdin?
If it helps, I am working with a compiler that accepts Objective-C. I also have the boost libraries available.
I've figured out the stdout part of the question. For posterity, this works:
static PyObject*
redirection_stdoutredirect(PyObject *self, PyObject *args)
{
const char *string;
if(!PyArg_ParseTuple(args, "s", &string))
return NULL;
//pass string onto somewhere
Py_INCREF(Py_None);
return Py_None;
}
static PyMethodDef RedirectionMethods[] = {
{"stdoutredirect", redirection_stdoutredirect, METH_VARARGS,
"stdout redirection helper"},
{NULL, NULL, 0, NULL}
};
//in main...
Py_Initialize();
Py_InitModule("redirection", RedirectionMethods);
PyRun_SimpleString("\
import redirection\n\
import sys\n\
class StdoutCatcher:\n\
def write(self, stuff):\n\
redirection.stdoutredirect(stuff)\n\
sys.stdout = StdoutCatcher()");
PyRun_SimpleString("some script");
Py_Finalize();
Still having trouble with stdin...
To process all available input inside Python I'd recommend the fileinput module.
If you want to handle input as line-by-line commands, (such as in an interactive interpreter), you might find the python function raw_input useful.
To redirect stdin using a similar helper class such as the ones you've used above, the function to override is readline, not read. See this link for more info on that (and also raw_input).
Hope this helps, Supertwang
Easiest way I found so far to do this is as follows:
PyObject *sys = PyImport_ImportModule("sys");
PyObject* io_stdout = PyFile_FromFile(stdout, "stdout", "a", nullptr);
PyObject_SetAttrString(sys, "stdout", io_stdout);
PyObject* io_stderr = PyFile_FromFile(stderr, "stderr", "a", nullptr);
PyObject_SetAttrString(sys, "stderr", io_stderr);
PyObject* io_stdin = PyFile_FromFile(stdin, "stdin", "r", nullptr);
PyObject_SetAttrString(sys, "stdin", io_stdin);
you can test it with:
# for test
PyRun_SimpleString("print sys.stdin.readline()");
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