How to creating python module from C

How to creating python module from C

C always provide light-weight processing among all high-level programming language. Using python give advantages which we can extend into C as python modules. There are several workflow we should know before starting.

1. Naming Convention
Preferable we create C files always followed with module to indicating it’s a “Module”.
Eg:

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temperaturemodule.c

2. Using Python Dev API
We should have “python-dev” installed in our Linux or Ubuntu.
Then we can call Python API to wrap C codes as python modules.

3. Use setup.py
Because we will treat C extension as python modules, we should provide setup.py installation.

At this example, I will show how to write “temperature” module in C and extend into python as module.

First, we create temperaturemodule.c. Then we build design by :

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#INCLUDE HEADER

#CREATE METHOD fahrenheit_to_celcius

#CREATE METHOD celcius_to_fahrenheit

#REGISTER ALL METHODS

#INITIALIZE

1. #INCLUDE HEADER
We should call python header “Python.h”

2. #CREATE METHOD fahrenheit_to_celcius and #CREATE METHOD celcius_to_fahrenheit
We create to function to convert fahrenheit to celcius and vice-versa.

3. #REGISTER ALL METHODS
Then we should register all methods

4. #INITIALIZE
The last thing, we should initialize this modules.

The codes :

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#include <Python.h>

static PyObject* fahrenheit_to_celcius(PyObject* self, PyObject* args)
{
    double fahr, celcius;

    if(PyArg_ParseTuple(args, "d", &fahr)) {
        celcius = 5 * (fahr-32) / 9;
        return PyFloat_FromDouble(celcius);
    } else {
        return NULL;
    }
}

static PyObject* celcius_to_fahrenheit(PyObject* self, PyObject* args)
{
    double celcius, fahr;

    if(PyArg_ParseTuple(args, "d", &celcius)) {
        fahr = (9 * celcius / 5) + 32;
        return PyFloat_FromDouble(fahr);
    } else {
        return NULL;
    }
}
static PyMethodDef TemperatureMethods[] =
{
    {"celcius_fahrenheit", celcius_to_fahrenheit, METH_VARARGS, ""},
    {"fahrenheit_celcius", fahrenheit_to_celcius, METH_VARARGS, ""},
};

PyMODINIT_FUNC

inittemperature(void)
{
    (void) Py_InitModule("temperature", TemperatureMethods);
}

Then, we should create “setup.py” for installation :

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from distutils.core import setup, Extension

module1 = Extension("temperature", sources=["temperaturemodule.c"])

setup (name = "FahrenheitCelcius",
      version = "1.0",
      description = "Convert Fahrenheit value into Celcius and vice-versa",
      ext_modules = [module1]
)

After we have “temperaturemodule.c” and “setup.py”, we can start build this C into python module :

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python build setup.py
cd build/<lib>/

On folder which contain “temperature.so”, we can execute python intepreter and start import this module by :

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Python 2.7.2+ (default, Oct  4 2011, 20:06:09)
[GCC 4.6.1] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import temperature
>>> f = 100
>>> c = temperature.fahrenheit_celcius(f)
>>> c
37.77777777777778
>>> f = temperature.celcius_fahrenheit(c)
>>> f
100.0

All codes can be easily grab at my github in :
https://github.com/yodiaditya/C

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