Just making sure it is out there, if you are using setters and getters (like the set_amount(n)) you are using you shouldn’t be able to do it the first way.
So it’s a property of Object Oriented Languages to have a private class(where you can’t access the property by Class.property because duh, Private Class) you have a public method in that class that sets and gets the value for that property.
So by all means go by KND2501’s suggestion. KISS(Keep it Simple Stupid) all the way