There are a number of places in Objects/stringobject.c where memory is 
allocated for a string of length n using:

PyObject_MALLOC(sizeof(PyStringObject) + n)

On my computer (OS X 10.5.5/Intel), and, I suspect, on most common 
platforms, the PyStringObject struct is going to contain some number of 
bytes (probably 3) of trailing padding;  the result is that the 
PyObject_MALLOC call above asks for 3 more bytes than are necessary, and 
on average the Python interpreter will waste 3 bytes of memory per string 
allocation.  Is there any reason not to replace these calls with:

PyObject_MALLOC(offsetof(PyStringObject, ob_sval) + n + 1)

instead?

Patch attached.