3 numbers separated by a decimal
This method of notation indicates the sex(es) of the snakes of that particular species. The first number means male, second female, and third means the sex is unknown.
1.2.3 Ball Pythons - one male (1). two females (2). three unknown (3)
3.1.0 Rat Snake - three males (3). one female (1). zero unknown (0)
Sometimes you'll see four number (0.1.2.3) with the last one representing how many eggs are being incubated for that species.
Whenever you see this notation the males are always listed first, females second, unknown genders third, and eggs incubating fourth. This is the commonly accepted way to use this system of notation.