Develop Reference

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)

Embedding python in Visual C++

I am trying to embed python in a Visual C++ application using visual studio 2017.
I correctly included the header files path and the lib path from my Python 3.7.0 installation.
I can include the Python.h and pylifecycle.h files but get an error when I try to run the program. My code and error is below.
// TestPythonEmbedding.cpp : Defines the entry point for the console application.
//
#include "Python.h"
#include "pylifecycle.h"
#include "stdafx.h"
int main()
{
PyObject* myPointer;
Py_Initialize();
return 0;
}
Here are the errors I get when I try to build the solution.
testpythonembedding.cpp(11): error C2065: 'PyObject': undeclared
identifier
testpythonembedding.cpp(11): error C2065: 'myPointer': undeclared
identifier
testpythonembedding.cpp(13): error C3861: 'Py_Initialize': identifier
not found
1>Done building project "TestPythonEmbedding.vcxproj" -- FAILED.
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========
Strangely enough Visual studio gives information about Pyobject* and highlights it as if it is identified. I included an image of that.
image

Cython Compile Error: Python3 Compatibility

I am running Python 3.4.4 :: Anaconda 4.0.0 (x86_64) on OS X Yosemite. My Cython's version is 0.23.4. I'm trying to embed some very trivial Cython code test.pyx into C code testcc.c. The problem is, if I use python2.7-config then everything works well (Python 2.7 is the built-in version on OS X). However if I use python3.4-config the following errors raised:
Undefined symbols for architecture x86_64:
"_inittest", referenced from:
_main in testcc-b22dcf.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I have to use Python3 since all my other codes are written in it. Please help me solve this problem.
The following are my source files:
test.pyx:
cdef public void pythonAdd(int[] a):
a[1] = 5
a[0] = 4
testcc.c:
#include "Python.h"
#include "test.h"
#include <math.h>
#include <stdio.h>
int main(int argc, char **argv) {
Py_Initialize();
inittest();
int a [2] = {0 , 0};
pythonAdd(a);
printf("fist: %d, second: %d", a[0], a[1]);
Py_Finalize();
return 0;
}
And Compiling those two files using following setup.py:
from distutils.core import setup, Extension
from Cython.Build import cythonize
ext = Extension("testc", sources=["test.pyx"])
setup(name="testc", ext_modules=cythonize(ext))
The following is the command I compile those c files:
ldflags:=$(shell $(python3.4-config) --ldflags)
cflags:=$(shell $(python3.4-config) --cflags)
python setup.py build_ext --inplace
cython test.pyx
gcc $(cflags) $(ldflags) test.c testcc.c -o cysvm.out
Update:
I changed the inittest() to PyInit_test() as Jim suggested. The code compiles successfully. However when I run ./cysvm.out the following errors occured:
./cysvm.out
Could not find platform independent libraries <prefix>
Could not find platform dependent libraries <exec_prefix>
Consider setting $PYTHONHOME to <prefix>[:<exec_prefix>]
Fatal Python error: Py_Initialize: unable to load the file system codec
ImportError: No module named 'encodings'
Current thread 0x00007fff772f5300 (most recent call first):
Update
I solved this by adding the following line before Py_Initialize(); in my c code:
Py_SetPythonHome(L"/PATH/to/python3");

This is probably due to the fact that in Python 3.x initialization of modules is not performed by calling init<module_name> but rather with PyInit_<module_name> (See PEP 3121). So, if you are linking with Python 3.x and executing via 3.x you need to change the initialization call.
In short, changing the call that initializes the module from:
inittest();
To:
PyInit_test();
and recompiling, should do the trick.
As for your second problem, an alternate solution other than using Py_SetPythonHome is setting PYTHONHOME to the output of python3.4-config --exec-prefix (or sys.exec_prefix) prior to compilation.

Boost, Python: Linker error with Visual Studio 2015

I basically did the same as the person here:
Building/including Boost.Python in VS2013
However, I used an empty cpp file with only the main function and the inclusion of <boost/python.hpp>
#include <boost/python.hpp>
int main() {
return 0;
}
Now I get the strange linker error (in Visual Studio):
1>LINK : fatal error LNK1104: cannot open file 'boost_python-vc140-mt-gd-1_60.lib'
Which is strange, because I have the lib file I think, however, it is called:
libboost_python3-vc140-mt-gd-1_60.lib

You need to configure your Visual C++ project setting.
The following case operates well.
[debug platform mode] x64
[include directory] (..\;;);C:\boost\boost_1_60_0\;C:\Python35\include\; # add your actual boost and python directory path
[library directory] (..\;;);C:\Python35\libs\;C:\boost\boost_1_60_0\stage\lib; # add your actual boost and python library path

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.