__div__ is a function that takes two arguments, a numerator and denominator. The problem is that it can produce incorrect results when dividing two numbers that are not both integers.
def __div__(self, other): return self.value / other.value
This is a Python method definition. It is defining a method called __div__ that takes two arguments, self and other. The method will return the result of self.value divided by other.value.
__truediv__
In Python, the truediv function returns the true division (integer division) of two integers.
__floordiv__
In Python, the floor() function returns the lowest integer value not greater than the argument.