object oriented programming in python.ppt

Python Mini-Course
University of Oklahoma
Department of Psychology
Lesson 25
The object-oriented thought process
6/16/09
Python Mini-Course: Lesson 25
1

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
6/16/09
2

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
6/16/09
3

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
6/16/09
4

What is an object?
Objects have two components:
Data (i.e., attributes)
Behaviors (i.e., methods)
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5

Object attributes
Store the data for that object
Example (taxi):
Driver
OnDuty
NumPassengers
Location
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6

Object methods
Define the behaviors for the
object
Example (taxi):
PickUp
DropOff
GoOnDuty
GoOffDuty
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7
•GetDriver
•SetDriver
•GetNumPassengers

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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8

Object implementation
The user does NOT need to know
how the method works internally
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9

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
6/16/09
10

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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11

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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12

Inheritance
You can create new classes by
abstracting out common
attributes and behaviors from a
parent (or base) class
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13

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14

Is-a relationship
Because sub-classes inherit from
their base class, they have an is-
a relationship:
Lion is a cat
Cat is a mammal
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15

Polymorphism
Allows similar objects to to
respond to the same message
(method call) in different
manners
Sub-classes can override base
class methods
6/16/09
16

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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17

Composition
Objects can contain other objects
This is called a has-a relationship
Example:
 Taxi has-a driver
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18

object oriented programming in python.ppt

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