Helloworld with Python C extension

[MRAB]

On 2016-08-29 18:30, Ganesh Pal wrote:
>  Hello Team ,
>
> I need you input on the below  hello world program.  I a m trying to add a
> python binding which will return the character for the given index .  I am
> on Python 2.7   and linux
>
> Example :
>>> string ='helloworld'
>>>dda_hello(5)
>>> 'w'
>
>
>  /*
> + * Hello world example for python bindings
> + */
> +
> +static char* string = "helloworld";
> +char dda_hello(int i)
> +     {
> +      return string[i];
> +     }
> +
> +static PyObject *
> +py_dda_hello(PyObject *self, PyObject *args )
> +{
> +       int index;
> +       char char1;
> +       if (!PyArg_ParseTuple(args, "i", &index))
> +               return NULL;
> +       char1 = dda_hello(index);

This bit is wrong:

> +       return Py_BuildValue("s",char1);

The format "s" is for a null-terminated C string (char *), but you're 
giving it a C int.

The format you should be using is "c" (C int representing a character).

> +}
> +
> +/*
>
> @@ -1674,6 +1705,10 @@ PyMethodDef xyz_methods[] = {
> +        {"dda_hello", py_dda_hello, METH_VARARGS,
> +                "Returns the character entered for a given index"},
>
>
>>>>  import as.ds.dss as daa
>>>> print dda.dda_hello(1)
> zsh: segmentation fault (core dumped)  python
>
> Apologies for posting the diff  , I didn't find a better way
>
It would be a good idea to check the index and raise an exception if 
it's out the bounds.