Embedding Python within C++ (CPython API)

Question

I'm trying to embed Python within my C++ project (Qt5). My project looks like this:

python_test.pro:

QT += core
QT -= gui

TARGET = python_test
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += main.cpp

INCLUDEPATH += C:\Tools\Python\Python35_64\include

LIBS += -LC:\Tools\Python\Python35_64\ -lpython3

main.cpp:

#include <Python.h>
#include <QCoreApplication>

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    Py_Initialize();
    PyRun_SimpleString("from time import time,ctime\n"
                   "print('Today is', ctime(time()))\n");
    Py_Finalize();
    return a.exec();
}

When compiling I get a linker error telling me this: main.cpp:-1: Error: undefined reference to `__imp_PyRun_SimpleStringFlags'.

The funny thing is that Py_Initialize() and Py_Finalize() can be found. I read something about the define Py_LIMITED_API which hides the function PyRun_SimpleStringFlags. But I don't get it.

How am I supposed to run a Python script/file/string without these functions being available within the C API?

Setup:

Win7 Prof 64 bit
Qt 5.5.1
g++.exe (Rev1, Built by MSYS2 project) 5.3.0
Python 3.5.1 64-bit (prebuilt from https://www.python.org/downloads/release)/python-351/)

It may make a difference if you link -lpython35 and not -lpython3. — J.J. Hakala
– J.J. Hakala, Commented Jan 26, 2016 at 10:57
[offtopic] I would suggest to look at pythonqt (pythonqt.sourceforge.net) it's a really powerful way to bind Qt applications and python (it's PyQt the other way round) — bibi
– bibi, Commented Jan 26, 2016 at 11:06
@bibi I already have taken a look at this library and it seems perfect. But I had problems compiling it/debugging projects with this library included. Tried to contact the developers but didn't get an answer. So I decided to stick to CPython API since I need only to run scripts for converting strings. — Burner
– Burner, Commented Jan 26, 2016 at 11:47

J.J. Hakala · Accepted Answer · 2016-01-26 10:59:30Z

1

I tested this on my computer (without Qt though), with -lpython35 compiling succeeded and with -lpython3 it did not.

So

LIBS += -LC:\Tools\Python\Python35_64\ -lpython35

instead of

LIBS += -LC:\Tools\Python\Python35_64\ -lpython3

answered Jan 26, 2016 at 10:59

J.J. Hakala

6,2546 gold badges29 silver badges64 bronze badges

Sign up to request clarification or add additional context in comments.

3 Comments

Burner Over a year ago

This did the job, thank you! Is it correct that python3 (python3.dll) creates the define Py_LIMITED_API to keep API compatibility over all python 3 versions (3.2, 3.4 etc) ?

J.J. Hakala Over a year ago

@Burner If you put #define Py_LIMITED_API in your source file before #include <Python.h>, and then try to compile, you will notice that function PyRun_SimpleString won't be available and python3.dll corresponds to this limited API.

Burner Over a year ago

Thanks for the explanation! I'm now facing a problem while deploying my application to another pc. The application starts fine but as soon as a script is executed (PyRun_SimpleString is reached) the application crashes with an error within the file: C:\windows\system32\ucrtbase.dll. The dll is available on all the PCs I'm working at. I don't know what to make of it.

Collectives™ on Stack Overflow

Embedding Python within C++ (CPython API)

1 Answer 1

3 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

3 Comments

Your Answer

Sign up or log in

Post as a guest

Related