Learning Python, 6th Edition

Chapter 11. Assignments, Expressions, and Prints

Now that we’ve had a first introduction to Python statement syntax, this chapter begins our in-depth tour of specific Python statements. We’ll begin with the basics: assignment statements, expression statements, and print operations. We’ve already seen all of these in action, but here we’ll fill in important details we’ve skipped so far. Although they’re relatively simple, as you’ll see, there are optional variations for each of these statement types that will come in handy once you begin writing realistic Python programs.

Assignments

We’ve been using the Python assignment statement for a while to retain objects in examples. In its basic form, you write the target of an assignment on the left of an equals sign, and the object to be assigned on the right. The target on the left may be a name or object component, and the object on the right can be an arbitrary expression that creates an object. For the most part, assignments are straightforward, but here are a few key properties to note up front:

• Assignments create object references. As discussed in Chapter 6, Python assignments store references to objects in names or data structure components. They always create references to objects instead of copying the objects. Because of that, Python variables are more like pointers than data storage areas.

• Names are created when first assigned. Python creates a variable name the first time you assign it a value (i.e., an object reference), ...