Python Program Structure Revisited

Another way to understand the role of statements is to revisit the concept hierarchy introduced in Chapter 4, which talked about built-in objects and the expressions used to manipulate them. This chapter climbs the hierarchy to the next level:

 

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  1. Programs are composed of modules.
  2. Modules contain statements.
  3. Statements contain expressions.
  4. Expressions create and process objects.

At its core, Python syntax is composed of statements and expressions. Expressions process objects and are embedded in statements. Statements code the larger logic of a program’s operation—they use and direct expressions to process the objects we studied in the preceding chapters. Moreover, statements are where objects spring into existence (e.g., in expressions within assignment statements), and some statements create entirely new kinds of objects (functions, classes, and so on). Statements always exist in modules, which themselves are managed with statements.