Python Threads do not run in C++ Application Embedded Interpreter

Question

I have a C++ application which uses embedded python interpreter with the Python C API. It can evaluate Python files and source code with PyRun_SimpleFile and PyObject_CallMethod.

Now I have a python source code which has a worked thread which subclasses threading.Thread and has a simple run re-implementation:

import time
from threading import Thread
class MyThread(Thread):
    def __init__(self):
        Thread.__init__(self)

    def run(self):
        while True:
            print "running..."
            time.sleep(0.2)

The problem is that the "running" is printed only once in the console.

How can I make sure that python threads keep on running parallel to my C++ applications GUI loop.

Thanks in advance,

Paul

Answer 1

I've had the same similar problem and found the solution. I know the thread is pretty old but just in case anybody is wondering... Here is a code sample that does what you need.

#include <Python.h>

#include <iostream>
#include <string>
#include <chrono>
#include <thread>

int main()
{
    std::string script =
        "import time, threading                        \n"
        "" 
        "def job():                                    \n"
        "    while True:                               \n"
        "         print('Python')                      \n"
        "         time.sleep(1)                        \n"
        ""
        "t = threading.Thread(target=job, args = ())   \n"
        "t.daemon = True                               \n"
        "t.start()                                     \n";

    PyEval_InitThreads();
    Py_Initialize();

    PyRun_SimpleString(script.c_str());

    Py_BEGIN_ALLOW_THREADS

    while(true)
    {
        std::cout << "C++" << std::endl;
        std::this_thread::sleep_for(std::chrono::milliseconds(1000));
    }

    Py_END_ALLOW_THREADS

    Py_Finalize();

    return 0;
}