Advanced Placement exams do have a scale [1, 5]. However, these values are represented on an ordinal scale, not on an intervallic or ratio scale.
The numeric types used by Python assume that the values used a fixed location for the value 0. This means this equality will hold:
x - y == (1 + x) - (1 + y)
Ordinal scale data does not fix the length/distance between integers so a comparable equality:
3 - 2 != 4 - 3
The issue is that the values only represent order (the inverse of rankings).