10 Object-Oriented Programming

Objectives

In this chapter you’ll:

• Create custom classes and objects of those classes.

• Understand the benefits of crafting valuable classes.

• Control access to attributes.

• Appreciate the value of object orientation.

• Use Python special methods __repr__, __str__ and __format__ to get an object’s string representations.

• Use Python special methods to overload (redefine) operators to use them with objects of new classes.

• Inherit methods, properties and attributes from existing classes into new classes, then customize those classes.

• Understand the inheritance notions of base classes (superclasses) and derived classes (subclasses).

• Understand duck typing and polymorphism that enable “programming in the general.”

• Understand class object from which all classes inherit fundamental capabilities.

• Compare composition and inheritance.

• Build test cases into docstrings and run these tests with doctest,

• Understand namespaces and how they affect scope.

Outline

1. 10.1 Introduction

2. 10.2 Custom Class Account

   1. 10.2.1 Test-Driving Class Account

   2. 10.2.2 Account Class Definition

   3. 10.2.3 Composition: Object References as Members of Classes

3. 10.3 Controlling Access to Attributes

4. 10.4 Properties for Data Access

   1. 10.4.1 Test-Driving Class Time

   2. 10.4.2 Class Time Definition

   3. 10.4.3 Class Time Definition Design Notes

5. 10.5 Simulating “Private” Attributes

6. 10.6 Case Study: Card Shuffling and Dealing Simulation

   1. 10.6.1 Test-Driving Classes Card and DeckOfCards

   2. 10.6.2 Class Card—Introducing Class Attributes

   3. 10.6.3 Class DeckOfCards

   4. 10.6.4 Displaying Card Images with Matplotlib

7. 10.7 Inheritance: Base Classes and Subclasses

8. 10.8 Building an Inheritance Hierarchy; Introducing Polymorphism

   1. 10.8.1 Base Class CommissionEmployee

   2. 10.8.2 Subclass SalariedCommissionEmployee

   3. 10.8.3 Processing CommissionEmployees and SalariedCommissionEmployees Polymorphically

   4. 10.8.4 A Note About Object-Based and Object-Oriented Programming

9. 10.9 Duck Typing and Polymorphism

10. 10.10 Operator Overloading

    1. 10.10.1 Test-Driving Class Complex

    2. 10.10.2 Class Complex Definition

11. 10.11 Exception Class Hierarchy and Custom Exceptions

12. 10.12 Named Tuples

13. 10.13 A Brief Intro to Python 3.7’s New Data Classes

    1. 10.13.1 Creating a Card Data Class

    2. 10.13.2 Using the Card Data Class

    3. 10.13.3 Data Class Advantages over Named Tuples

    4. 10.13.4 Data Class Advantages over Traditional Classes

14. 10.14 Unit Testing with Docstrings and doctest

15. 10.15 Namespaces and Scopes

16. 10.16 Intro to Data Science: Time Series and Simple Linear Regression

17. 10.17 Wrap-Up

1. Exercises