Object Oriented Programming

Question 1

An object is an instance and has:

Answer 1

• a type
• an internal data representation
• each instance is a particular type of object

Question 2

Objects

Answer 2

• A data abstraction that capture
• Can create new instances of objects
• Can destroy objects

Question 3

Data abstraction captures

Answer 3

• internal representation

- interface for interacting with objects through methods (procedures)

Question 4

Creating a class

Answer 4

• defining the class name

- defining the class attributes

Question 5

Using the class

Answer 5

• creating new instances of objects

- doing operations on the instance

Question 6

Advantage of OOP

Answer 6

• Bundle data into packages together with procedures (functions)
• Divide-and-conquer development
• Classes make it easy to reuse code

Question 7

Divide-and-conquer development

Answer 7

• implement and test behavior of each class separately
• increase modularity reduces complexity
• inheritance allows sub-classes to redefine or extend a subset of a super-class behavior

Question 8

Method is

Answer 8

A function that works only with THIS class

Question 9

More about methods

Answer 9

Python always passes the actual object as the first argument to use as ‘self’

Question 10

The “.” operator is used to:

Answer 10

Access any attribute:

• a data attribute of an object
• a method of an object

Question 11

Class is

Answer 11

A blueprint created by a programmer for an object

Question 12

Object is

Answer 12

An instance of a class

Question 13

Power of OOP

Answer 13

• bundle objects together
• use abstractions (how to implements vs. how to use)
• build layers of object abstractions
• create own classes of objects

Question 14

Implementing class
vs
using class

Answer 14

write code from two different perspectives

Question 15

Implementing an object

Answer 15

• define the class
• define the data attributes
• define methods

Question 16

Using an object

Answer 16

• create instances of object type

- do operations

Question 17

Class def. of an object

Answer 17

• class is the type
• class is defined generically (use self)
• common across all instances

Question 18

Instance of a class

Answer 18

• one particular object
• data values vary between instances
• structure of the class

Question 19

Why use OOP and classes of objects?

Answer 19

• mimic real life

- group different objects as part of the same type

Question 20

Groups of objects have attributes

Answer 20

• data attributes

- procedural attributes

Question 21

Data attributes

Answer 21

• how can you represent your object with data

- what it is

Question 22

Procedural attributes

Answer 22

Behavior/operations/methods

• what kind of things can you do with the object?
• what it does

Question 23

Instance of DOT notation

Answer 23

• instantiation creates an instance of an object
• dot notation used to access attributes
• better to use getters and setters!

Question 24

Information hiding

Answer 24

• may change data attribute var. names
• getting an error if:
  accessing data attributes outside class and class definition changes

Question 25

getters and setters

Answer 25

use a.get_xxx() NOT a.xxx - good style - easy to maintain code - prevent bugs

Question 26

Python not great at information hiding

Answer 26

- allows you to access data from outside - allows you to write to data from outside - allows you to create data attributes for an instance from outside - it's not good style to do any of these!

Question 27

self and other args

Answer 27

- self determined from instance | - default arguments for formal parameters

Question 28

Hierachies

Answer 28

- parent class (super class) | - child class (sub class)

Question 29

Child class

Answer 29

- inherits all data and behaviors - add more info - add more behavior - override behavior

Question 30

Which method to use

Answer 30

- subclass can have methods with the same name as super class - subclass can have methods with the same name as other sub classes - look for method name in current class def - if not found -> look up the hierarchy - use first method up the hierarchy

Question 31

variables can be?

Answer 31

``` instance variables or class variables ```

Question 32

Instance variables

Answer 32

- specific to an instance - created for each instance (belongs to an instance) - used the generic variable name 'self' within the class def.

Question 33

Class variables

Answer 33

- belongs to a class - defined inside class - but outside the class __init__ methods - shared among all objects/instances of that class

Question 34

Summary of classes and OOP

Answer 34

- bundle together objects - common attributes and procedures - use abstraction to make a distinction between - how to implement - how to use - build layers of object abstractions - create our own classes of objects