Run compiled python script with arguments in C++ (Cython)

Question

What I try to achieve is compiling my Python script to lib/dll and invoke it with arguments.

This is my setup.py file for the script:

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

setup(
    ext_modules = cythonize("nu3k2nu4k.py")
)

Used this command to produce compilation outputs:

python setup.py build_ext --inplace

following files produced:

nu3k2nu4k.c
nu3k2nu4k.cp36-win_amd64.pyd
nu3k2nu4k.pyx

and a subdirectory named build which contains:

nu3k2nu4k.cp36-win_amd64.exp
nu3k2nu4k.cp36-win_amd64.lib
nu3k2nu4k.obj

How can I invoke the compiled script from c++ code with arguments?

I used Cython for the task but that's not mandatory, boost or others could be used as well (I'm doing this to make the source code not accessible).

Edit:

Using the documentation provided by Mykola Shchetinin I have managed to generate an API header file for my script. I basically added a cdef api keyword to my main function. While this does help me export the method name to c++ I still need a way to pass around some arguments to my script. Since I pass string arguments I was hoping for a similar way like using PyRun to set argv and parse the arguments from the script (since I would like to avoid conversion of strings from c to python encoding if possible) Is there any easy way to pass those string arguments?

EDIT 2:

I got it working! following the sample provided by Mykola and directly compiling the c file output instead of using the .lib I got it working.

It is actually in the docs: cython.readthedocs.io/en/latest/src/userguide/… — Mykola Shchetinin
– Mykola Shchetinin, Commented Oct 15, 2017 at 8:43
From the documentation it seems like I need to add a cdef api keyword to my main function in order to produce the header file needed. I'll give it a shot... — Or Groman
– Or Groman, Commented Oct 15, 2017 at 9:29
I managed to create an API header file for my script. Is there any way to set the the arguments like in PyRun? declaring the arguments as c types seems like a one ugly way for dealing with conversions from c strings to python and I would like to avoid that if possible... — Or Groman
– Or Groman, Commented Oct 15, 2017 at 10:13
I suggest you updating your question with what you achieved to make it easier to answer for other users. I have just pointed out what I have found in the docs... — Mykola Shchetinin
– Mykola Shchetinin, Commented Oct 15, 2017 at 10:16

Community · Accepted Answer · 2020-06-20 09:12:55Z

1

I have tried to do that by myself. So I convert char * to bytes in cython. (according to docs)

That is what I came up with. I have the following setup (gcc and centos7.2):

setup.py

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

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

main.c

#include "Python.h"
#include "func.h"

int main() {
    Py_Initialize();
    initfunc();
    func("0123hello jorghy!!");
    Py_Finalize();
    return 0;
}

func.pyx

cdef public func(char * arg):
    cdef bytes py_bytes = arg
    print(str(py_bytes));

I build all this stuff with the following commands:

python setup.py build_ext --inplace

gcc -I/usr/include/python2.7 -lpython2.7 -Wall -Wextra -O2 -g -o test main.c func.c

Then when running the executable file test I get the following results:

0123hello jorghy!!

UPDATE

There is another way to approach this problem:

I have created a cython file test.pyx:

import sys

if __name__ == "__main__":
    print("hei")
    print(sys.argv)

And compiled as an executable it using commands:

cython test.pyx --embed
gcc -I/usr/include/python2.7 -lpython2.7 -Wall -Wextra -O2 -g -o test test.c

Then you can call this code as an executable file:

$ ./test 1 2 3
hei
['./test', '1', '2', '3']

Then you can call it from C++ using std::system or other (better) methods.

edited Jun 20, 2020 at 9:12

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answered Oct 15, 2017 at 13:40

Mykola Shchetinin

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5 Comments

Mykola Shchetinin Over a year ago

The behaviour is the same when I do not use str() call inside print()

Or Groman Over a year ago

I have tried to follow this example and did the same for me. I have created same setup.py and func.pyx and compiled it the same for the first method. I used this code to invoke the function: Py_Initialize(); PyInit_func(); func("0123hello jorghy!!"); Py_Finalize(); I linked visual studio with the libary file produced from Cython and there was a linkage compilation error. the method signature was not exported to the lib file. When I tried to do similar method with api keyword instead of public it did compile but I got an exception. Thanks for the help with this.

Or Groman Over a year ago

I'm trying to solve the exception/ compilation error in visual studio. I'll update what I got soon.

Mykola Shchetinin Over a year ago

Probably something regarding Python.h, python2.7 libraries. I had to add -I/usr/include/python2.7 -lpython2.7 arguments to my gcc compiler to avoid linkage errors (I use centos7.2). There should be something similar for visual studio C++ compiler on stackoverflow.

Or Groman Over a year ago

Ok! so I got it working when instead of using the lib file produced by Cython I did the same as you and directly compiled the .c file output. I got it working for a small sample project so I'll implement it in my project as well in no time. I have marked your answer as accepted, thanks for all the help.

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