important distinction needs to be made between mutable and immutable objects. Mutable object's such as lists can have their values changed. They have methods, such as insert() or append(), that change an objects value. Immutable objects, such as strings, cannot have their values changed, so when we run their methods, they simply return a value rather than change the value of an underlying object. We can, of course, use this value by assigning it to a variable or using it as an argument in a function