How to catch Python 3 stdout in C++ code - python-3.x

Question

In an old question about how to catch python stdout in C++ code, there is a good answer and it works - but only in Python 2.
I would like to use something like that with Python 3. Anyone could help me here?
UPDATE
The code I am using is below. It was ported from Mark answer cited above, the only change was the use of PyBytes_AsString instead of PyString_AsString, as cited in documentation.
#include <Python.h>
#include <string>
int main(int argc, char** argv)
{
std::string stdOutErr =
"import sys\n\
class CatchOutErr:\n\
def __init__(self):\n\
self.value = ''\n\
def write(self, txt):\n\
self.value += txt\n\
catchOutErr = CatchOutErr()\n\
sys.stdout = catchOutErr\n\
sys.stderr = catchOutErr\n\
"; //this is python code to redirect stdouts/stderr
Py_Initialize();
PyObject *pModule = PyImport_AddModule("__main__"); //create main module
PyRun_SimpleString(stdOutErr.c_str()); //invoke code to redirect
PyRun_SimpleString("print(1+1)"); //this is ok stdout
PyRun_SimpleString("1+a"); //this creates an error
PyObject *catcher = PyObject_GetAttrString(pModule,"catchOutErr"); //get our catchOutErr created above
PyErr_Print(); //make python print any errors
PyObject *output = PyObject_GetAttrString(catcher,"value"); //get the stdout and stderr from our catchOutErr object
printf("Here's the output:\n %s", PyBytes_AsString(output)); //it's not in our C++ portion
Py_Finalize();
return 0;
}
I build it using Python 3 library:
g++ -I/usr/include/python3.6m -Wall -Werror -fpic code.cpp -lpython3.6m
and the output is:
Here's the output:
(null)
If someone needs more information about the question, please let me know and I will try provide here.

Answer 1

Your issue is that .value isn't a bytes object, it is a string (i.e. Python2 unicode) object. Therefore PyBytes_AsString fails. We can convert it to a bytes object with PyUnicode_AsEncodedString.
PyObject *output = PyObject_GetAttrString(catcher,"value"); //get the stdout and stderr from our catchOutErr
PyObject* encoded = PyUnicode_AsEncodedString(output,"utf-8","strict");
printf("Here's the output:\n %s", PyBytes_AsString(encoded));
Note that you should be checking these result PyObject* against NULL to see if an error has occurred.