Class inheritance

Object-Oriented Programming in Python

Alex Yarosh

Content Quality Analyst @ DataCamp

Code reuse

1. Someone has already done it

Modules are great for fixed functionality
OOP is great for customizing functionality

logos of several python packages

Code reuse

1. Someone has already done it

2. DRY: Don't Repeat Yourself

various gui elements

Code reuse

1. Someone has already done it

2. DRY: Don't Repeat Yourself

don't use various gui elements

Inheritance

$$\Large{\text{New class functionality = Old class functionality + extra}}$$

account class

savings account inherited from account

two classes inherited from account

modified method in checking account

Implementing class inheritance

class BankAccount:
    def __init__(self, balance):
       self.balance = balance

    def withdraw(self, amount):
        self.balance -= amount

# Empty class inherited from BankAccount
class SavingsAccount(BankAccount):
    pass

class MyChild(MyParent):
   # Do stuff here

MyParent: class whose functionality is being extended/inherited
MyChild: class that will inherit the functionality and add more

Child class has all of the the parent data

# Constructor inherited from BankAccount
savings_acct = SavingsAccount(1000)
type(savings_acct)

__main__.SavingsAccount

# Attribute inherited from BankAccount
savings_acct.balance

# Method inherited from BankAccount
savings_acct.withdraw(300)

Inheritance: "is-a" relationship

A SavingsAccount is a BankAccount

(possibly with special features)

savings_acct = SavingsAccount(1000)
isinstance(savings_acct, SavingsAccount)

True

isinstance(savings_acct, BankAccount)

True

acct = BankAccount(500)
isinstance(acct,SavingsAccount)

False

isinstance(acct,BankAccount)

True

Let's practice!

Object-Oriented Programming in Python