Simple Python extension in Nim?

[matkuki]

Hi guys,

I want to make a simple Python3 extension in Nim. I used the **Nim Backend 
Integration** 
([http://nim-lang.org/docs/backends.html#interfacing-backend-code-calling-nim](http://forum.nim-lang.org///nim-lang.org/docs/backends.html#interfacing-backend-code-calling-nim))
 example as a starting point.

The example crashes when trying to **echo** the arguments passed from the C 
wrapper to the Nim procedure in the **nim_module.nim** file line 5. When 
commenting out that line the extension module works! Can anyone tell me why?

I'm using Windows Vista x64, Python 3.4.1 x64, Nim 0.14.3 x64.

Compiling everything with MSVC 2010.

The Nim file **nim_module.nim**: 
    
    
    import math
    
    proc cos_func*(number: cdouble): cdouble {.exportc.} =
        echo "You're in Nim!"
        echo number # <-- This line crashes Python
        result = math.cos(number)
    

It's compiled with 
    
    
     nim c --noMain --noLinking --header:nim_module.h nim_module.nim

The Python wrapper file **nim_wrapper.c**: 
    
    
    #include <stdio.h>
    #include <Python.h>
    #include "nim_module.h"
    
    /*  wrapped cosine function */
    static PyObject* first_func(PyObject* self, PyObject* args)
    {
        double value;
        double answer;
        
        /*  parse the input, from python float to c double */
        if (!PyArg_ParseTuple(args, "d", &value))
            return NULL;
        /* if the above function returns -1, an appropriate Python exception 
will
         * have been set, and the function simply returns NULL
         */
        
        /* call cos in Nim */
        answer = cos_func(value);
        
        /*  construct the output from cos, from c double to python float */
        return Py_BuildValue("f", answer);
    }
    
    /*  define functions in module */
    static PyMethodDef nim_methods[] =
    {
         {"first_func", first_func, METH_VARARGS, "evaluate the cosine in Nim"},
         {NULL, NULL, 0, NULL}
    };
    
    static struct PyModuleDef nim_module =
    {
        PyModuleDef_HEAD_INIT,
        "nim_wrapper", /* name of module */
        "",          /* module documentation, may be NULL */
        -1,          /* size of per-interpreter state of the module, or -1 if 
the module keeps state in global variables. */
        nim_methods
    };
    
    /* module initialization */
    PyMODINIT_FUNC
    PyInit_nim_wrapper(void)
    {
        return PyModule_Create(&nim_module);
    }
    

and the **setup.py** script: 
    
    
    import os
    from distutils.core import setup, Extension
    
    nim_c_files = []
    items = os.listdir("nimcache/")
    for i in items:
        if i.endswith(".c"):
            nim_c_files.append("nimcache/" + i)
    
    nim_module = Extension(
        'nim_wrapper',
        sources = [
            'nim_wrapper.c',
        ] + nim_c_files,
        extra_compile_args = [
            "-Ipath\\to\\app\\nimcache",
            "-IC:\\Nim\\lib",
        ],
    )
    
    # run the setup
    setup(ext_modules=[nim_module])
    

Building the module with: 
    
    
     python3 setup.py build_ext --inplace 

The test script is: 
    
    
    import nim_wrapper
    
    print(nim_wrapper.first_func(100))