Editing Advanced Scripting (section)

==== More Complex Unpacking ====
If you're dealing with simple scalars, then you might be able to skip this portion.

Now, we should have access to the data the user sent us, in '''listA''' and '''listB,''' and it should be there and be clean.  But, not forgetting that '''listA''' and '''listB''' are list of 3D coordinates, let's unpack them further into sets of coordinates.  Because we know the length of the lists, we can do something like the following:

<source lang="c">
       // make space for the current coords; pcePoint is just a float[3]
       pcePoint coords = (pcePoint) malloc(sizeof(cePoint)*length);

       // loop through the arguments, pulling out the
       // XYZ coordinates.
       int i;
       for ( i = 0; i < length; i++ ) {
               PyObject* curCoord = PyList_GetItem(listA,i);
               Py_INCREF(curCoord);
       
               PyObject* curVal = PyList_GetItem(curCoord,0);
               Py_INCREF(curVal);
               coords[i].x = PyFloat_AsDouble(curVal);
               Py_DECREF(curVal);

               curVal = PyList_GetItem(curCoord,1);
               Py_INCREF(curVal);
               coords[i].y = PyFloat_AsDouble(curVal);
               Py_DECREF(curVal);

               curVal = PyList_GetItem(curCoord,2);
               Py_INCREF(curVal);
               coords[i].z = PyFloat_AsDouble(curVal);
               Py_DECREF(curVal);

               Py_DECREF(curCoord);
        }

 ... more code ...
</source>

Where, '''pcePoint''' is just a float[3].  Line 2 just gets some memory ready for the 3xlenght list of coordinates.  Then, for each item for 1..length, we unpack the list using '''[http://docs.python.org/api/listObjects.html PyList_GetItem]''', into '''curCoord'''.  This then gets further unpacked into the float[3], '''coords'''.

We now have the data in C++/C data structures that the user passed from PyMOL.  Now, perform your task in C/C++ and then return the data to PyMOL.