Fundamentals of Programming. October 15, 2017

Transcription

1 Fundamentals of Programming October 15, 2017

2 Life Lesson If you re twenty-two, physically fit, hungry to learn and be better, I urge you to travel as far and as widely as possible. Sleep on floors if you have to. Find out how other people live and eat and cook. Learn from them wherever you go. - Anthony Bourdain

3 What are we doing today? Overview of Object Oriented Programming Writing user defined classes

4 Data Types We have used the following types of variables so far int Float bool String Lists Variables are used to store values

5 User-Defined types What if we want to model something more complex? A Vehicle A Bank Account An Image A Rectangle A Ball

6 Data and Actions Each of these types have properties and functions associated with them What kind of properties does a vehicle have? Color Speed Engine Size Number of Passengers

7 Actions What kind of functions are associated with a vehicle? Start Stop changespeed

8 Modeling a Vehicle How would be model a vehicle in python? One way it to declare a variable for each property V1Speed V1Color V1NumPass This will become really tedious if we have several vehicles

9 Defining classes Another solution is to define a type called Vehicle that will encompass all these properties

10 Vehicle Class #Defining a class class Vehicle( ): def init (self): self.color = "White" self.speed = 0.0 self.numpassengers = 4 # using this class mycar = Vehicle() print mycar.speed

11 Defining Functions in a class class Vehicle( ): def init (self): self.color = "White" self.speed = 0.0 self.numpassengers = 4 def changespeed(self, delta): self.speed = self.speed + delta

12 Using functions of a class mycar = Vehicle() print mycar.speed mycar.changespeed(50) print mycar.speed mycar.changespeed(25) print mycar.speed

13 Adding more functions change speed only if car is started class Vehicle(object): def init (self): self.speed = 0.0 self.numpassengers = 4 self.started = False def changespeed(self, delta): if self.started: self.speed = self.speed + delta def start(self): self.started = True def stop(self): self.started = False self.speed = 0

14 Let s work on this problem Design a data type that is able to model a bank account

15 Objects Each object has a set of attributes E.g., Andrew Edward + First name + Last name + address +Age In OOP, we often refer to these attributes as the fields of the object

16 Classes and Objects A class is a category of objects which share the same attributes An object is an item that belongs to a class An object is an instance of a class Example: Person Class All Persons have attributes first name, last name, address, and age Ali Bashir is an instance of the Person Class

17 Classes and Objects We can think of a class as the definition of its objects We can think of a class as a template We can think of a class a a blueprint of an object

18 Classes and Objects Consider a University class. Carnegie Mellon is an object of the University class or Carnegie Mellon is a University Georgetown is another object of this class or Georgetown is a University

19 Classes and Objects This is called an is a relationship [object] is a [class] Robocop is a Robot Hello World is a String Exploring Python is a book My Toyota RAV4 is a car

20 Classes and Objects A class has 3 parts: a name Fields/attributes methods Members of a class

21 Fields or Attributes E.g. A Course class might have fields coursecode, coursetitle, and creditvalue is an object of the Course class What are the field values for ? What fields would a Student class have? What fields would a BankAccount class have?

22 Methods Methods are procedures and functions that perform actions Sometimes called behaviours Methods are the actions your objects will perform, such as calculations, displaying, sorting, etc. Methods for a Course class could include: getcoursename(), and setcreditvalue();

23 Methods What methods would a Student class have? What methods would a BankAccount class have? Who will be calling these methods? The caller of a method is referred to as the client