Revisiting the Building Blocks: Python Classes and Object-Oriented Essentials

Lesson Overview

Greetings! Today, we're revisiting Python classes, the core building block of Object-Oriented Programming (OOP) in Python. Through hands-on examples, we'll revisit the fundamental concepts of Python classes, including their structure, attributes, and methods.

Python Classes Refresher

Let's begin with a refresher on Python classes. Essential to OOP, Python classes bundle relevant data and functions into compact units called objects. Consider a video game character, which is a typical example of a class instance, with specific attributes (such as health or strength) and methods (such as attack or defense). Python class GameCharacter: # constructor method def __init__(self, name, health, strength): self.name = name # attribute self.health = health # attribute self.strength = strength # attribute def attack(self, other_character): # method other_character.health -= self.strength Python classes facilitate the grouping of associated code elements, simplifying their management. Now, to better remind ourselves how the above example works, let's go through it step-by-step.

Structure of a Python Class

A Python class serves as a blueprint consisting of attributes and methods. While attributes represent data relevant to a class instance, methods are actions or functions that manipulate this data. Each class includes an__init__function, also known as a constructor, which is used to define class attributes. An essential keyword within these methods is self, which represents the class instance. In object-oriented programming, it's needed to access the class's attributes and methods. When a new class instance is created, Python automatically passes it to the self parameter to access individual instance attributes and methods using the self keyword. This mechanism allows each object to keep track of its own state and behaviors. Python class GameCharacter: # constructor: defines class attributes def __init__(self, name, health, strength): self.name = name # attribute self.health = health # attribute self.strength = strength # attribute character = GameCharacter("Hero", 100, 20) # object or instance of the class class GameCharacter: # constructor: defines class attributes def __init__(self, name, health, strength): self.name = name # attribute self.health = health # attribute self.strength = strength # attribute character = GameCharacter("Hero", 100, 20) # object or instance of the class

Class Attributes

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Python

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

character = GameCharacter("Hero", 100, 20)  # object or instance of the class

Python

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

character = GameCharacter("Hero", 100, 20)  # object or instance of the class
print(character.name)  # prints: Hero
print(character.health)  # prints: 100
print(character.strength)  # prints: 20

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

character = GameCharacter("Hero", 100, 20)  # object or instance of the class
print(character.name)  # prints: Hero
print(character.health)  # prints: 100
print(character.strength)  # prints: 20

Python

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

    def attack(self, other_character):  # method
        other_character.health -= self.strength  # modifies 'other_character's health attribute

character_1 = GameCharacter("Hero", 100, 20)   # First instance of GameCharacter
character_2 = GameCharacter("Villain", 80, 15)  # Second instance

print(character_2.health)  # prints: 80
character_1.attack(character_2)  # character_1 attacks character_2
print(character_2.health)  # prints: 60, health decreased after attack

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

    def attack(self, other_character):  # method
        other_character.health -= self.strength  # modifies 'other_character's health attribute

character_1 = GameCharacter("Hero", 100, 20)   # First instance of GameCharacter
character_2 = GameCharacter("Villain", 80, 15)  # Second instance

print(character_2.health)  # prints: 80
character_1.attack(character_2)  # character_1 attacks character_2
print(character_2.health)  # prints: 60, health decreased after attack

Python

# Define the BankAccount class
class BankAccount:
    # Constructor with a default balance of 0
    def __init__(self, holder_name, balance=0):
        self.holder_name = holder_name
        self.balance = balance

    # Method to deposit money
    def deposit(self, amount):
        if amount > 0:
            self.balance += amount
            print(f"{amount} deposited. New balance: {self.balance}")
        else:
            print("Deposit amount must be positive.")

    # Method to withdraw money
    def withdraw(self, amount):
        if 0 < amount <= self.balance:
            self.balance -= amount
            print(f"{amount} withdrawn. Remaining balance: {self.balance}")
        else:
            print("Insufficient balance for the withdrawal or amount is not positive.")

# Create an instance of BankAccount
account = BankAccount("Alex", 1000)  # An account with initial balance of 1000

# Perform some transactions
account.deposit(500)  # Deposit money
account.withdraw(200)  # Withdraw money
print(f"Final balance in {account.holder_name}'s account: {account.balance}")

# Define the BankAccount class
class BankAccount:
    # Constructor with a default balance of 0
    def __init__(self, holder_name, balance=0):
        self.holder_name = holder_name
        self.balance = balance

    # Method to deposit money
    def deposit(self, amount):
        if amount > 0:
            self.balance += amount
            print(f"{amount} deposited. New balance: {self.balance}")
        else:
            print("Deposit amount must be positive.")

    # Method to withdraw money
    def withdraw(self, amount):
        if 0 < amount <= self.balance:
            self.balance -= amount
            print(f"{amount} withdrawn. Remaining balance: {self.balance}")
        else:
            print("Insufficient balance for the withdrawal or amount is not positive.")

# Create an instance of BankAccount
account = BankAccount("Alex", 1000)  # An account with initial balance of 1000

# Perform some transactions
account.deposit(500)  # Deposit money
account.withdraw(200)  # Withdraw money
print(f"Final balance in {account.holder_name}'s account: {account.balance}")

Python

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

character = GameCharacter("Hero", 100, 20)  # object or instance of the class
print(character.name)  # prints: Hero
print(character.health)  # prints: 100
print(character.strength)  # prints: 20

Python

class GameCharacter:
    # constructor: defines class attributes
    def __init__(self, name, health, strength):  
        self.name = name       # attribute
        self.health = health   # attribute
        self.strength = strength   # attribute

    def attack(self, other_character):  # method
        other_character.health -= self.strength  # modifies 'other_character's health attribute

character_1 = GameCharacter("Hero", 100, 20)   # First instance of GameCharacter
character_2 = GameCharacter("Villain", 80, 15)  # Second instance

print(character_2.health)  # prints: 80
character_1.attack(character_2)  # character_1 attacks character_2
print(character_2.health)  # prints: 60, health decreased after attack

Python

# Define the BankAccount class
class BankAccount:
    # Constructor with a default balance of 0
    def __init__(self, holder_name, balance=0):
        self.holder_name = holder_name
        self.balance = balance

    # Method to deposit money
    def deposit(self, amount):
        if amount > 0:
            self.balance += amount
            print(f"{amount} deposited. New balance: {self.balance}")
        else:
            print("Deposit amount must be positive.")

    # Method to withdraw money
    def withdraw(self, amount):
        if 0 < amount <= self.balance:
            self.balance -= amount
            print(f"{amount} withdrawn. Remaining balance: {self.balance}")
        else:
            print("Insufficient balance for the withdrawal or amount is not positive.")

# Create an instance of BankAccount
account = BankAccount("Alex", 1000)  # An account with initial balance of 1000

# Perform some transactions
account.deposit(500)  # Deposit money
account.withdraw(200)  # Withdraw money
print(f"Final balance in {account.holder_name}'s account: {account.balance}")

Lesson Overview

Python Classes Refresher

Structure of a Python Class

Class Attributes

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Class Methods

Examples of Python Classes, Attributes, and Methods

Lesson Summary and Practice