Chapter 17. Scopes

Chapter 16 introduced basic function definitions and calls. As we saw, Python’s basic function model is simple to use, but even simple function examples quickly led us to questions about the meaning of variables in our code. This chapter moves on to present the details behind Python’s scopes—the places where variables are defined and looked up. As we’ll see, the place where a name is assigned in our code is crucial to determining what the name means. We’ll also find that scope usage can have a major impact on program maintenance effort; overuse of globals, for example, is a generally bad thing.