Intermediate Python
===================

Python C Extensions
````````````````````

Few use-case where writing C extension for Python might make sense include:

1. Integrating with existing C library
2. Performance Optmizations

Creating C Extensions
~~~~~~~~~~~~~~~~~~~~~

.. code-block:: c

    #include <Python.h>

    static PyObject*
    say_hello(PyObject* self, PyObject* args)
    {
        const char* name;

        if (!PyArg_ParseTuple(args, "s", &name))
            return NULL;

        printf("Hello %s!\n", name);

        Py_RETURN_NONE;
    }

    static PyMethodDef HelloMethods[] =
    {
        {"say_hello", say_hello, METH_VARARGS, "Greet somebody."},
        {NULL, NULL, 0, NULL}
    };

    PyMODINIT_FUNC
    inithello(void)
    {
        (void) Py_InitModule("hello", HelloMethods);
    }


As mentioned in `TutorialsPoint Guide <https://www.tutorialspoint.com/python/python_further_extensions.htm>`_, there are four things we require

1. Include `Python.h`, this gives access to Python's internal APIs
2. `C function` you want to expose as interface from module {In our example about it is `static PyObject *say_hello(PyObject* self, PyObject* args)`}
3. Mapping of `Python function names` to `C function names` {In our case `HelloMethods`}
4. An initialization function  {In our case it is `inithello`}

Creating setup.py file
~~~~~~~~~~~~~~~~~~~~~~

`setup.py` file will be responsible for building the module.

.. code-block:: python

    from distutils.core import setup, Extension

    module1 = Extension('hello', sources = ['hellomodule.c'])

    setup (name = 'PackageName',
            version = '1.0',
            description = 'This is a demo package',
            ext_modules = [module1])

Following is how to build and use the module, on shell

.. code-block:: sh

    python setup.py install

On terminal

.. code-block:: python

    >>> from hello import say_hello
    >>> say_hello("sidharth")

Note: If you're interested in extending Python using `C++`, `pybind11 <https://pybind11.readthedocs.io/en/stable/basics.html>`_ seems to be a good option