OOP Concepts

Object-oriented Programming

​What?

• Define an abstract “class” with attributes and functions

• Objects are instances of this class

• They can “inherit” these attributes and functions

• But these can be changed as necessary!​

​Why?

• Might have multiple different instances (objects) which behave “similarly”

• Have similar (but not same) attributes and functions

• Allows us to reuse code without replicating

• Also reduces points of error! ​

• ​Taxonomy always helps

​How?

• Define a “parent” class, e.g. mammals

• ​Some common attributes, e,g. title, habitat

• ​Can define instances, e.g. dog, elephant, blue whale

• ​Each of these has a title and a habitat

• The __init__ function for the class specifies how to initialize instances

​Example

class mammals:

………… title = “”

………… habitat = “”​

………… def __init__(self, title, habitat) :

………………………. self.title = title​

………………………. self.habitat = habitat​

​………… def showatt(self) :

…………………print(self.title, self.habitat, sep=“ lives in ”)

​dog = mammals(“dog”, “kennel”)

ele = mammals(“elephant”, “forest”)

​Inheritance

• What if I want to define classes which only share some attributes?

• Consider a class for people. All people have a name and an age.

• Now consider a class for UCSC students. Students are people (too?), but they have an ID number, and their GPA so far.

• However, consider a class for people who are UCSC employees. They have an ID, but no GPA. Instead, they have a designation.

• But both students and employees have all the people attributes!​

• Enter inheritance!​

​Inheritance

class people:

………… nm = “”

………… age = 0​

………… def __init​__(self, name, age):

………………… self.​nm = name

​………………… self.age = age

……….. def intro(self):

…………………..print(“Hi, my name is ”, self.nm, “ and I’m ”, self.age, “ years old”)​

​Inheritance

class student(people):

………… def __init​__(self, name, age, gpa):

………………… self.​nm = name

​………………… self.age = age

………………… self.gpa​ = gpa

……….. def intro(self):

…………………..print(“Hi, my name is ”, self.nm, “ and I’m ”, self.age, “ years old, and my GPA is ”, gpa)

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​Inheritance

class employee(people):

………… def __init​__(self, name, age, desig):

………………… self.​nm = name

​………………… self.age = age

………………… self.desig​ = desig

……….. def intro(self):

…………………..print(“Hi, my name is ”, self.nm, “ and I’m ”, self.age, “ years old, and my designation is ”, desig)

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