It might be useful to know that the question is exploring the concept of associative array or associative memory. Python has a special built-in data structure for this named Dictionary. A Python Dictionary stores a collection of associated data: keys and values. In this example, the keys are the integers, while the values are the names of the days (strings). According to the Python documentation ( https://docs.python.org/3/tutorial/datastructures.html ) the main operations on a Python Dictionary are storing some value with an associated key, and retrieving a value given its associated key. While this example doesn't really require it, in some applications it would be beneficial to use this built-in capability rather than write all the code for inserting, enforcing unique keys, sorting, removing entries etc from scratch. Cheers.