Retrieving start and end point coordinates with ArcPy?

How do I retrieve start and end point coordinates with ArcPy for a polyline feature class?

I expect to pass a segment identifier to a subroutine and have it pass back start and end coordinates. The Field Calculator method doesn't work for me, because I need the value for other calculations that can't be performed within it. (I also prefer not to change the data to store these coordinates as attributes.) I am attempting to calculate address ranging for a "center out" addressing scheme. The address value depends on the distance to the "county center".