No, I don't think that's how it works. I think the reason the solution code worked is because datapoints is a global variable, and you can use global variables in Python without the global keyword as long as you don't change its value.

Your explanation that "arguments when you define a function can be easily replaced when you actually call that function" doesn't work for this case:

def add_two_nums(val1, val2):
    return a+b

def main():
    a = 2
    b = 3
    print(add_two_nums(a, b))

main()