Develop Reference

Project File Line Suppression State Error LNK1104 cannot open file 'python310_d.lib'

I wrote a program for learning how to embed python in c++ . But when I try to run it in visual studio It shows a linker error that python310_d.lib is not found. I searched for this file in my python directory lib folder but there was no such file with this name. So now I need a way to somehow get that file. Please help me.
Here is my code
#include <iostream>
#include <Python.h>
using namespace std;
int main(int argc, char const* argv[])
{
Py_Initialize();
PyRun_SimpleString("print(\'Hellow Python\')");
Py_Finalize();
return 0;
}
Here are my errors
Severity Code Description Project File Line Suppression State
Error LNK1104 cannot open file 'python310_d.lib' Project1 C:\Users\noob\source\repos\Project1\Project1\LINK 1

It appears that the problem is you don't have the debug libraries installed. By default the installer will not install these unless you check the option to download these:
The picture and information for this answer was found in the following link:
https://github.com/pybind/pybind11/issues/3403#issuecomment-951485263

C++ python binding: failed to import cv2

I m using Ubuntu 20.04, python 3.8 and developing a C++ project in Qt Creator. I m trying to call a python file from C++ code. I have created an environment in conda and calling the py file. There is segmentation fault occurring when I m attempting to import cv2 module. Other modules like sys, numpy can be imported. cv2 is installed in the environment and can be accessed when I run python from cmd prompt.
Also I tried to run the python commands directly in a C++ file, like:
PyRun_SimpleString("import cv2");
But this also sends segmentation fault.
I tried giving path of the site-packages directory in CMakeLists.txt but it also resulted in same error.
mainwindow.cpp:
#include "mainwindow.h"
#include "./ui_mainwindow.h"
#include <stdio.h>
#include <pyhelper.hpp>
#include <string>
#include <iostream>
MainWindow::MainWindow(QWidget *parent)
: QMainWindow(parent)
, ui(new Ui::MainWindow)
{
ui->setupUi(this);
Py_InitializeEx(0);
PyRun_SimpleString("import cv2");
}
MainWindow::~MainWindow()
{
delete ui;
}
Qt Creator debugger stack trace is as below:

How do I compile a C program which includes Python.h on Windows?

I am trying to learn how to embed a Python interpreter into my C/C++ programs.
I like this concept because it may enable me to extend C programs at run time as well as enable users to write custom scripts/plugins.
Detailed instruction on embedding Python in C is provided at: https://docs.python.org/3/extending/embedding.html
I'm using example code provided in the Python documentation to figure out the mechanics involved:
embedded.c
#include <Python.h>
int
main(int argc, char *argv[])
{
Py_SetProgramName(argv[0]); /* optional but recommended */
Py_Initialize();
PyRun_SimpleString("from time import time,ctime\n"
"print 'Today is',ctime(time())\n");
Py_Finalize();
return 0;
}
The problem is I can't figure out how to compile it on Windows using gcc.
C:\Users\user\embedded_python> gcc embedded.c
embedded.c:2:10: fatal error: Python.h: No such file or directory
#include <Python.h>
^~~~~~~~~~
compilation terminated.
I think the problem is I need to link to the Python.h file, but I can't seem to get the compiler flags right:
C:\Users\user\Desktop\embedded_python>gcc -IC:\Users\user\AppData\Local\Programs\Python\Python38 -lPython38 embedded.c
embedded.c:2:10: fatal error: Python.h: No such file or directory
#include <Python.h>
^~~~~~~~~~
compilation terminated.
How can I get this program to compile on Windows (preferably with gcc/g++ to avoid Visual Studio bloat)?

In Linux, but I suppose if you activate your Bash from windows and can perform a work around. First you have to install python3-dev
Then use this command line where your file is located, to compile (test is your filename)
gcc -Wall test.c -o test $(pkg-config --cflags --libs python3)

Exposing C++ to Python error from BoostPython

I'm exposing a simple C++ code to Python through BoostPython library:
#include <boost/python/detail/wrap_python.hpp>
#include <boost/python.hpp>
using namespace boost::python;
bool test_api( void ){
return true;
};
BOOST_PYTHON_MODULE(materials) {
def( "test_api", test_api );
}
After I try to import this module, the python interpreter returns the error:
ImportError: ./example.so: undefined symbol: _Py_RefTotal
I've linked the module statically against the boost python library and the python dynamic libraries libpython3.2m.so and libpython3.2m.so.1.0 are present in the work directory.
Any suggestions on where to find the missing symbol?

The Boost libraries were not consistent with the Python installation.
cd boost_source
./bootstrap.sh --with-libraries=python --prefix=../boost_target
To configure Boost to point to the correct Python installation:
vim tools/build/v2/user-config.jam
Edit the line that points to the Python:
using python : version_number
: path_to_python_executable
: path_to_python_include_directory
: path_to_python_library_directory
Then, run the build system:
./b2

_Py_RefTotal is defined in object.h under a precompiler guard:
$less include/python3.6m/object.h
#ifdef Py_REF_DEBUG
PyAPI_DATA(Py_ssize_t) _Py_RefTotal;
...
...
#endif /* Py_REF_DEBUG */
I was linking python3.6m but including headers from include/python3.6dm. Fixed issue including ptyhon3.6m

Python.h not found while building sample application with cmake and pybind11

I want to build simple app with pybind11, pybind is already installed in my Ubuntu system with cmake (and make install). I use this simple cmake file:
cmake_minimum_required(VERSION 3.0 FATAL_ERROR)
project(trt_cpp_loader )
find_package(pybind11 REQUIRED)
add_executable(trt_cpp_loader main.cpp)
set_property(TARGET trt_cpp_loader PROPERTY CXX_STANDARD 11)
This is main.cpp:
#include <iostream>
#include <pybind11/embed.h>
namespace py = pybind11;
using namespace std;
int main(){return 0;}
when I build it, I get:
In file included from /usr/local/include/pybind11/pytypes.h:12:0,
from /usr/local/include/pybind11/cast.h:13,
from /usr/local/include/pybind11/attr.h:13,
from /usr/local/include/pybind11/pybind11.h:44,
from /usr/local/include/pybind11/embed.h:12,
from /home/stiv/lpr/trt_cpp_loader/main.cpp:2:
/usr/local/include/pybind11/detail/common.h:112:10: fatal error: Python.h: No such file or directory
#include <Python.h>
^~~~~~~~~~
compilation terminated.
how can I fix this problem? (python-dev and python3-dev are already installed, Python.h is available)

You'll want to use the pybind11_add_module command (see https://pybind11.readthedocs.io/en/stable/compiling.html#building-with-cmake) for the default case of creating an extension module.
If the goal is indeed to embed Python in an executable, it is your reponsibility to explicitly add python headers & libraries to the compiler/linker commands in CMake. (see https://pybind11.readthedocs.io/en/stable/compiling.html#embedding-the-python-interpreter on how to do that)

Following the Wenzel Jakob's answer I want to put an example of CMakeLists.txt for compiling the example provided in this tutorial:
// example.cpp
#include <pybind11/pybind11.h>
int add(int i, int j) {
return i + j;
}
PYBIND11_MODULE(example, m) {
m.doc() = "pybind11 example plugin"; // optional module docstring
m.def("add", &add, "A function which adds two numbers");
}
and
# example.py
import example
print(example.add(1, 2))
and
# CMakeLists.txt
cmake_minimum_required(VERSION 2.8.12)
project(example)
find_package(pybind11 REQUIRED)
pybind11_add_module(example example.cpp)
now in the root run
cmake .
make
now run the python code by
python3 example.py
P.S. I have also written some instructions here for compiling/installing the pybind11.

Maybe just install the Python headers? For example, on Ubuntu you can install the sudo apt-get install python-dev (or python3-dev or pythonX.Y-dev) package. That could resolve this.