Now that you have a general idea of Big-O notation and the differences between the different functions, our goal in this section is to tell you about the Big-O performance for the operations on Python lists and dictionaries. We will then show you some timing experiments that illustrate the costs and benefits of using certain operations on each data structure. It is important for you to understand the efficiency of these Python data structures because they are the building blocks we will use as we implement other data structures in the remainder of the book. In this section we are not going to explain why the performance is what it is. In later chapters you will see some possible implementations of both lists and dictionaries and how the performance depends on the implementation.