It is not a Coastal. It is a Darwin Carpet (aka Northern or North-western Carpet). This a currently considered a subspecies of carpet python and given the scientific name Morelia spiltota variegata. The term “het” is short for heterozygous. If it is a guaranteed het, as it sounds like, the animal is carrying two different genes for a given characteristic. In the case of Darwin pythons, the characteristic is colouration and it carries one copy of the gene for normal colouration and the other copy is for albino colouration. If your het bred with another het, there is a 25% probability an offspring being albino, 50% of being het, and 25% of being normal Darwin. If bred with an albino Darwin, there is a 50% probability of any given offspring being albino, and 50% of it being guaranteed het.
A very nice like looking snake.