ToDay

Introducing how to use Cython as a way to call Python from C / C ++.

It is common to write Sotobori in Python and call the core part C / C ++ for speeding up. This time it is ** reverse **. On the contrary, there is not much clue other than the official document ... Please let me know if you have any. OTL.

(Addition: I wrote the Mac version.)

-Call the code generated by Cython from C / C ++ (Mac version)

environment

--Windows is used as the OS because Visual Studio is used.

IDE Visual Studio 2017 Community ――It is not necessary to limit it to Community, 2017. I was able to go in 2013, so I think it's OK in 2015.
Python3.5.4（Miniconda3)
Cython 0.26

Creating an environment with Visual Studio

Solution creation

Visual C ++-> Select an empty project-> Press the OK button for the time being. Now you can create an empty project. The solution and the name of the first project created is Project1.

Add code to source file

Add an empty C ++ file with Ctrl + Shift + A. The default name is Source.cpp, but use it as it is. We will write the code in Source.cpp later. For now, leave it blank.

Know the location of Python

Please note that from here on, it will depend on your environment.

I think readers are familiar with Python, so you know which Python you are using. But let's check.

Open a command prompt

> where python

Is executed. In my case it was C: \ ProgramData \ Miniconda3 \ python.exe.

Go to C: \ ProgramData \ Miniconda3. In the picture below, ʻinclude and libs` are selected.

Make a note of the path of this directory as it will be used next.

Property editing

Add the full path of include noted above to Properties> VC ++ Directory> Include Directory. In my case C: \ ProgramData \ Miniconda3 \ include is.

Add the full path of libs noted above to Properties> VC ++ Directory> Include Directory. In my case C: \ ProgramData \ Miniconda3 \ libs is.

Let's make it look like the red frame surrounded by the figure below. Also, set the platform to x64.

Introduction of debug binaries and debugging symbols

Get the installer from the official Python homepage and launch the installer. Click Customize installation and then click the Next button.

Check download debug binaries, debugging symbols. If you do not use this Python as the main, you do not need to add PATH.

Build check

Write the following in Source.cpp

`source.cpp`


#include<Python.h>
int main() {
	Py_Initialize();
	printf("Hello");
	Py_Finalize();
	return 0;
}

If you can build in release mode, it's OK for the time being. If you get angry that Python.h is missing, adding the include directory has failed. Let's calm down and set it again.

And in debug mode, you need a DLL with the same name as python35_d.lib, so you need to get it.

I cannot find python35_d.lib

You can get it by starting the Python3 installer from the official Python page and selecting "download debug binaries" as an option, referring to the above stack overflow. Let's find it.

Cython code creation

Create the following in the same layer as Source.cpp created above.

setup.py
cytest.pyx

Each code is as follows.

`setup.py`


from distutils.core import setup 
from Cython.Build import cythonize

setup(ext_modules=cythonize("cytest.pyx"))

`cytest.pyx`


from libc.stdio cimport printf

cdef public struct Point:
    double x
    double y

cdef public Point DoubleCoord(Point p):
    cdef Point q
    q.x=2*p.x
    q.y=2*q.x
    printf("q.x=%f, q.y=%f\n",q.x,q.y)
    return q

For the time being, I made a function in Cython that defines a vertex structure and doubles the coordinates and returns it.

setup Open a command prompt and build your Cython code.

> python setup.py build_ext --inplace

Add generation code

Generated at this time Add cytest.c cytest.h to the Visual Studio source and header files respectively.

Edit Source.cpp

`Source.cpp`


#include<Python.h>
#include<stdio.h>
#include "cytest.h"

int main() {
	Py_Initialize();
	struct Point p;
	p.x = 3.5;
	p.y = 7.0;
	struct Point q = DoubleCoord(p);
	printf("q.x=%f,q.y=%f", q.x, q.y);
	Py_Finalize();
}

As a result so far, it should be as shown in the figure below on Visual Studio.

When executed, it will be as follows.

Finally

It's hard ... As a reference

[Interfacing with External C Code] (http://cython.readthedocs.io/en/latest/src/userguide/external_C_code.html)

I will mention.

[PYTHON] Call the code generated by Cython from C / C ++ (Windows version)