The typing dot final, when this was added in three eight reason they discovered that yes, super nice. So the example in the Python docs says there's a max size capital max capital size, instead is just saying it's colon final 9000. Now, that means nothing to Python. But it means something to type checkers, right? If you have like my pie or something, and somebody tries to change the value of it later, it's going to come at least as a linting type of error if not a full on runtime error. Another idea that I think comes in that's pretty interesting is the sentinel pattern, where you come up with a particular number and sort of