[osullivj]

http://plato.stanford.edu/entries/rigid-designators/

A rigid designator designates the same object in all possible worlds. Translation to software terms: a safe pointer/reference refers to the same object in all possible process lifetimes. Consider Python: everything is an object, including integers. If you look into the C implementation of CPython you'll see that the runtime creates certain commonly used object up front, rather than on demand as is the case for most objects. IIRC integers 0 to 10 are created upfront. So if we exec 'i = 0' in Python and don't change i then i refers to the same object every time we execute. It's a rigid designator!