3.6 Itse1359-1440-class variables

Table of contents

• Preface
  • What you have learned
  • What you will learn
  • Viewing tip
    • Figures
    • Listings
• General background information
• Discussion and sample code
  • Late modification of class
    • A simple class definition
    • Instantiate and display two objects
    • Add a class variable directly
    • Add a class variable via an object
    • Display both class variables via one object
    • Display both class variables via the other object
  • Typical class variable usage
    • The class definition
    • Instantiate two objects from the class
    • Modify class variable using object
    • Modify the class variable using the class name
    • A word of caution is in order
  • Shadowing or hiding a class variable
    • Class definition with a shadowing method
    • Instantiate and display classVar in two objects
    • Modify classVar in one object
    • Modify the contents of the class variable
• Run the programs
• Visualize the programs
• Complete program listings
• Miscellaneous

Preface

This module is one in a collection of modules on Python designed for teaching ITSE 1359 Introduction to Scripting Languages: Python at Austin Community College in Austin, TX.

What you have learned

Earlier modules provided

• an overview of classes and objects in Python,
• an explanation of the self word in Python class definitions, and
• a detailed explanation of instance variables in Python class definitions.

You have also learned that although other OO languages such as Java and C++use terminology that is common with Python terminology, such as class , object , class variable , and instance variable , those terms have significantly different meanings in Python than they do in many otherOO languages.

What you will learn

I promised in an earlier module that I would revisit and explain the difference between class variables and instance variables in classes and objects. An earlier module explained instance variables in detail.You will learn some of the details regarding class variables in this module.

Viewing tip

I recommend that you open another copy of this module in a separate browser window and use the following links to easily find and view the Figuresand the Listings while you are reading about them.

(Note to blind and visually impaired students: most of the Figures and all of the Listings inthis module are presented in plain text format and should be accessible using an audio screen reader or a braille display. Note however that the requiredindentation may not be properly represented by an audio screen reader.)

Figures

• Figure 1 . Output from the code in Listing 2.
• Figure 2 . Output of the code in Listing 5.
• Figure 3 . Output from the code in Listing 7.
• Figure 4 . Output from the code in Listing 8.
• Figure 5 . Output from the code in Listing 9.
• Figure 6 . Output from the code in Listing 10.
• Figure 7 . Output from the coded in Listing 12.
• Figure 8 . Output from the code in Listing 13.
• Figure 9 . Output from the code in Listing 14.
• Figure 10 . Output from the code in Listing 15.
• Figure 11 . Output from the code in Listing 16.
• Figure 12 . Output from the code in Listing 17.