Learning Python, 3rd Edition

Chapter 11. rwordsAssignment, Expressions, and print

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

Assignment Statements

We’ve been using the Python assignment statement for a while to assign objects to names. 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 computes an object. For the most part, assignments are straightforward, but here are a few properties to keep in mind:

• 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 variable names the first time you assign them a value (i.e., an object reference), so there’s no need to predeclare ...