Develop Reference

Specity C++ compiler in setup.py for Pybind11

This is a simple question but has been bothering me for 3 months now. When I use the setuptools/setup.py method to compile C++ code into a Python package on my windows os, it always defaults to MSVC, but part of the code uses stdlibc++ which is only accessible with GNU. Is there some way to specify it to MinGW, or somehow change the default behavior? I have looked into other methods, cppimport does not support windows, and the cmake method seems very complex to me.
For reference, a simple test to check whether the compiler is MSVC:
check_compiler.cpp
#include <iostream>
#include <pybind11/pybind11.h>
#include <pybind11/numpy.h>
#include <pybind11/stl.h>
namespace py = pybind11;
void test(){
#ifdef _MSVC_LANG
py::print("Compiled with MSVC. ");
#else
py::print("Not compiled with MSVC. ");
#endif
}
PYBIND11_MODULE(check_compiler, m) {
m.def("test", &test);
}
setup.py
"""
python setup.py install
"""
from pybind11.setup_helpers import Pybind11Extension
from setuptools import setup
import os
import shutil
ext_modules = [
Pybind11Extension(
'check_compiler',
sources=['check_compiler.cpp'],
language='c++',
cxx_std=11
),
]
setup(
name='check_compiler',
author='XXX',
ext_modules=ext_modules
)
# copy the package
for filename in os.listdir("dist"):
if filename.endswith(".egg"):
shutil.copy(os.path.join("dist", filename), ".")
Then run python setup.py install, an .egg file will be copied from subfolder to the current directory. Finally, run the following:
main.py
import check_compiler
check_compiler.test()
Similar question, but no accepted answer: How can I build a setup.py to compile C++ extension using Python, pybind11 and Mingw-w64?
Update: I was able to specify MinGW with cmake by adding -G "MinGW Makefiles" in the camke command. Still woudl welcome an answer of how to do this with setuptools, as it is the most convenient method.

How do I properly link python extension modules in C++?

I have a simple example python extenstion I want to use from C/C++. The code is as follows
example.pxy:
from numpy import random
cdef public void somefunc():
print(random.randint(500))
setup.py:
from setuptools import setup
cfom Cython.Build import cythonize
import numpy
setup(
ext_modules=cythonize("example.pyx"),
zip_safe=False,
include_dirs=[numpy.get_include()]
)
Running python3 setup.py build_ext --inplace --compiler="mingw32" -DMS_WIN64 then creates example.c, example.h and example.cp310-win_amd64.pyd. The C++ code I am using to call someFunc is:
example.cpp:
#include <Python.h>
#include "example.h"
int main()
{
Py_Initialize();
somefunc();
return 0;
}
This I compile using g++ example.cpp -DMS_WIN64. But that command seems to be incomplete. There are sill objects left that need to be linked, namely the ones from the example.pyx. How do I do this? I do not see any generated .dllor.lib` or similar.
Additionally, if I use #include "exmaple.c" in
example.cpp, I get a very long list of missing symbols from the linker. The objects are all named __im_Py*.
I am using MINGW64 on Windows 10. The python installation I am trying to link against is a regular python installation from the system. I have an environment variable CPLUS_INCLUDE_PATH=C:\Program Files\Python310\include.

ModuleNotFoundError python wrapper with c++

I am trying to reproduce the Boost.Python tutorial on how to do a wrap a C/C++ file for python.
This is the cpp file which builded successfuly.
#include "boost/python.hpp"
class SaySomething
{
public:
void set(std::string msg)
{
this->msg = msg;
}
std::string greet()
{
return msg;
}
std::string msg;
};
BOOST_PYTHON_MODULE(SaySomething)
{
namespace python = boost::python;
python::class_<SaySomething>("SaySomething")
.def("greet", &SaySomething::greet)
.def("set", &SaySomething::set)
;
}
In the same directory of the source code I have the python file
import SaySomething
msg = SaySomething.SaySomething()
msg.set('howdy')
msg.greet()
When I try to run the python file this error occurs
ModuleNotFoundError: No module named 'SaySomething'
I tried moving the compiled library to the same folder with no success. The tutorial doesn't elaborate on how to make the C++ file seen by the interpreter.
Edit
As some have suggested I have edited the extension of the compiled shared library to .pyd so python can see it. This creates a second error
ImportError: DLL load failed: The specified module could not be found.
This issue is exactly like mine. The solution suggests to add Boost.python to environnement variable. I know how to add path to this but I'm not sure what path I want, the boost.python dlls (or lib)? Just boost?

possible to compile python.exe without Visual Studio, with MinGw

I am trying to achieve things laid out on this page:
https://blogs.msdn.microsoft.com/pythonengineering/2016/04/26/cpython-embeddable-zip-file/
The code I am trying to compile is just this:
#include "Python.h"
int
wmain(int argc, wchar_t **argv)
{
return Py_Main(argc, argv);
}
In VisualStudio 15 I have to add the python/include and link to the python libs directories in the project and also add:
#include "stdafx.h"
and then it compiles and works fine. I'm just curious, is it possible to do this with mingw, or another open source C/C++ compiler?
If I place a file my_python.cpp which contains the following:
#include "include/Python.h"
int
wmain(int argc, wchar_t **argv)
{
return Py_Main(argc, argv);
}
in the root directory of a fresh 32-bit python 3.5 install (windows 7 x64), cd to that directory and try to run:
gcc my_python.cpp -Llibs -lpython35 -o my_python.exe
I get this error:
c:/mingw/bin/../lib/gcc/mingw32/5.3.0/../../../libmingw32.a(main.o):(.text.startup+0xa0): undefined reference to `WinMain#16'
Any way to fix this, get it running without Visual Studio?

The error is unrelated to Python. wmain is Visual Studio specific. GCC does not treat wmain as entry point, it just sits there as a function which never gets called.
GCC requires main or WinMain as entry point. If neither of those entry points is found, then the compiler will complain. So let's just use main as entry point.
Py_Main presumably expects wide character string input. CommandLineToArgvW will always provide that. Example:
#include <Windows.h>
#include "include/Python.h"
int main()
{
int argc;
wchar_t** argv = CommandLineToArgvW( GetCommandLineW(), &argc );
return Py_Main(argc, argv);
}
If you still get the same error, just provide WinMain entry point to make it happy
#include <Windows.h>
#include "include/Python.h"
int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
int argc;
wchar_t** argv = CommandLineToArgvW( GetCommandLineW(), &argc );
return Py_Main(argc, argv);
}
Also note, *.lib files are usually for Visual Studio. GCC version expects library names with *.a extension.

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.