Add PyBytes_FromStringAndSize() example

Author: vstinner

peps/pep-0782.rst

@@ -320,6 +320,34 @@ Create the bytes string ``b"Hello World"``::
     }
 
 
+Update ``PyBytes_FromStringAndSize()`` code
+-------------------------------------------
+
+Example of code using the soft deprecated
+``PyBytes_FromStringAndSize(NULL, size)`` API::
+
+        PyObject *result = PyBytes_FromStringAndSize(NULL, num_bytes);
+        if (result == NULL) {
+            return NULL;
+        }
+        if (safe_memcpy(PyBytes_AS_STRING(result), start, num_bytes) < 0) {
+            Py_CLEAR(result);
+        }
+        return result;
+
+It can now be updated to::
+
+        PyBytesWriter *writer = PyBytesWriter_Create(num_bytes);
+        if (writer == NULL) {
+            return NULL;
+        }
+        if (safe_memcpy(PyBytesWriter_GetData(writer), start, num_bytes) < 0) {
+            PyBytesWriter_Discard(writer);
+            return NULL;
+        }
+        return PyBytesWriter_Finish(writer);
+
+
 Reference Implementation
 ========================