Session 18 Preparation — Videos, Reading and Quizzes

• Here is the quiz in Microsoft Word in case you want to fill it in electronically in that format.
• Defining Classes and Objects
  • Textbook reading: Sections 9.1-9.6 — Objects and Classes (pages 444-460). You saw many of these ideas "by example" in your Session 16 class; now it is time to look at the details.
    • As you read, focus your attention on:
      • Overview and terminology (Section 9.1).  After reading this, you should be able to give a basic definition, in your own words, of the terms class, public interface, and encapsulation.  These terms will be elaborated in subsequent sessions of this chapter.
      • Instance variables and self (pages 447-449). Instance variable is another name for what we have called a field. An object is an instance of its class, and so a variable that belongs to a particular object (something that each object form the class needs to remember about itself) is an instance variable.
      
      Also, an object needs a way of referring to itself. The special variable name self is used for this purpose.
      Section 9.2 has lots of details about both instance variables and self.
      • Public interfaces, mutators and accessors (section 9.3).
      • The public and private parts of a class (page 454).  Python does not enforce this (other languages, such as Java, C++, and C#, do), but it is still a good idea.
      • What is the purpose of a class's constructor? (section 9.5)  Why should yo never call __init__ directly?  How are default and named arguments useful when writing constructors (and functions in general)?
      • Implementing Methods (Section 9.6) WHy do we need to use self so much in the body of a method?  How to call a method within a method (for the same object, for a different object).
      • Only define a class's instance variables in the constructor (page 460)
      • Class variable (a variable that belongs to the class, rather than having one variable for each object of that class) (page 460).