Some questions about C extensions

[Duncan Grisby]

In article <etdu2f69rhz.fsf at w20-575-109.mit.edu>,
 Alex  <cut_me_out at hotmail.com> wrote:

>-- Deallocation of memory for strings returned by python functions:
>   Do I have to do it, or is it somehow taken care of?  If I have
>   something like 
>
>      if (!PyArg_ParseTuple (args, "s", &sequence)) {
>           return NULL;}
>
>   do I have to do a free (sequence); at some point?  I would have
>   thought so, but it seems to be giving me a Seg fault.

No -- sequence points to the string which is inside the Python string
object.

>-- Reference counts for elements of brand new tuples.  Why do I have to
>   do a Py_INCREF on an object before I assign it to a new tuple with
>   PyTuple_SetItem?  Since it seems as though you have to do a Py_INCREF
>   every time anyway, is there a function like PyTuple_SetItem that will
>   do it for you?  The comment in the C API manual about this is very
>   cryptic, BTW.

You don't necessarily have to do Py_INCREF when you insert things in a
tuple. I often write code which does something like:

  PyObject *a, *b, *t;

  a = PyInt_FromLong(1234);
  b = PyString_FromString("Hello");
  t = PyTuple_New(2);
  PyTuple_SetItem(t, 0, a);
  PyTuple_SetItem(t, 1, b);

  /* ... do something with the tuple... */

  Py_DECREF(t);

That way, when the tuple is deleted, the int and string objects inside
it are also deleted.

Cheers,

Duncan.

-- 
 -- Duncan Grisby  \  Research Engineer  --
  -- AT&T Laboratories Cambridge          --
   -- http://www.uk.research.att.com/~dpg1 --