Transcript Day 01 - Lesson 4 - The University of Oklahoma

Lesson 25
The object-oriented thought process
Python Mini-Course
University of Oklahoma
Department of Psychology
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Lesson objectives
1. Define the key terms used in object-
oriented programming (OOP)
2. Understand the difference between
an object and a class
3. Describe the types of relationships
that are possible between objects
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Procedural vs. OOP
 Review from Lesson 6
 Procedural programming separates
the program operations and the data
 Object-oriented programming
packages the program operations
and the data together in object
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What is an object?
 The building blocks of an O-O
program
 A program that uses O-O is basically
a collection of objects
 Objects interact much like things in
the real world do
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What is an object?
 Objects have two components:
 Data (i.e., attributes)
 Behaviors (i.e., methods)
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Object attributes
 Store the data for that object
 Example (taxi):
 Driver
 OnDuty
 NumPassengers
 Location
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Object methods
 Define the behaviors for the
object
 Example (taxi):
 PickUp
 DropOff
 GoOnDuty
•GetDriver
•SetDriver
•GetNumPassengers
 GoOffDuty
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Object interface
 To use a method, the user
(programmer) must know:
 Name of the method
 Parameters to pass to the method
 What (if anything) the method
returns
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Object implementation
 The user does NOT need to know
how the method works internally
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What is a Class?
 A blueprint for an object
 Classes can be thought of as
templates or cookie cutters
 Given a class description, we can
instantiate objects of that class
 Classes are high-level data types
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OOP concepts
 Encapsulation
 Data and behaviors are packaged
together, but the object only reveals
the interfaces needed to interact
with it
 Internal data and behaviors can
remain hidden
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OOP concepts
 Interfaces
 Fundamental means of
communication between objects
 Should completely describe to user
(programmer) how to interact with
the object
 Should control access to attributes
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Inheritance
 You can create new classes by
abstracting out common
attributes and behaviors from a
parent (or base) class
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Is-a relationship
 Because sub-classes inherit from
their base class, they have an isa relationship:
 Lion is a cat
 Cat is a mammal
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Polymorphism
 Allows similar objects to to
respond to the same message
(method call) in different
manners
 Sub-classes can override base
class methods
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OOP example: animals.py
class Animal:
def __init__(self, name):
# Constructor of the class
self.name = name
class Cat(Animal):
def talk(self):
return 'Meow!'
class Dog(Animal):
def talk(self):
return 'Woof! Woof!'
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Composition
 Objects can contain other objects
 This is called a has-a relationship
 Example:
 Taxi has-a driver
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