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(python2.1-api.info)Examples

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Examples
========

Here is the example from section Note: Overview, rewritten so that
the I/O buffer is allocated from the Python heap by using the first
function set:

         PyObject *res;
         char *buf = (char *) PyMem_Malloc(BUFSIZ); /* for I/O */
     
         if (buf == NULL)
             return PyErr_NoMemory();
         /* ...Do some I/O operation involving buf... */
         res = PyString_FromString(buf);
         PyMem_Free(buf); /* allocated with PyMem_Malloc */
         return res;

The same code using the type-oriented function set:

         PyObject *res;
         char *buf = PyMem_New(char, BUFSIZ); /* for I/O */
     
         if (buf == NULL)
             return PyErr_NoMemory();
         /* ...Do some I/O operation involving buf... */
         res = PyString_FromString(buf);
         PyMem_Del(buf); /* allocated with PyMem_New */
         return res;

Note that in the two examples above, the buffer is always manipulated
via functions belonging to the same set. Indeed, it is required to use
the same memory API family for a given memory block, so that the risk
of mixing different allocators is reduced to a minimum. The following
code sequence contains two errors, one of which is labeled as _fatal_
because it mixes two different allocators operating on different heaps.

     char *buf1 = PyMem_New(char, BUFSIZ);
     char *buf2 = (char *) malloc(BUFSIZ);
     char *buf3 = (char *) PyMem_Malloc(BUFSIZ);
     ...
     PyMem_Del(buf3);  /* Wrong -- should be PyMem_Free() */
     free(buf2);       /* Right -- allocated via malloc() */
     free(buf1);       /* Fatal -- should be PyMem_Del()  */

In addition to the functions aimed at handling raw memory blocks from
the Python heap, objects in Python are allocated and released with
`PyObject_New()', `PyObject_NewVar()' and `PyObject_Del()', or with
their corresponding macros `PyObject_NEW()', `PyObject_NEW_VAR()' and
`PyObject_DEL()'.

These will be explained in the next chapter on defining and
implementing new object types in C.