Ch3. Python — Functions & Object-Oriented Programming

Functions

# Basic function
def greet(name, greeting="Hello"):
    """Return a greeting message."""
    return f"{greeting}, {name}!"

print(greet("Alice"))              # Hello, Alice!
print(greet("Bob", "Good morning")) # Good morning, Bob!

# Variable positional arguments (*args)
def sum_all(*numbers):
    return sum(numbers)

print(sum_all(1, 2, 3, 4, 5))  # 15

# Variable keyword arguments (**kwargs)
def print_info(**kwargs):
    for key, value in kwargs.items():
        print(f"{key}: {value}")

print_info(name="Alice", age=30, city="NYC")

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Lambda Functions

# Lambda: anonymous one-liner
square = lambda x: x ** 2
print(square(5))  # 25

# Use with sorted()
students = [("Alice", 92), ("Bob", 78), ("Charlie", 88)]
sorted_by_score = sorted(students, key=lambda x: x[1], reverse=True)
# [('Alice', 92), ('Charlie', 88), ('Bob', 78)]

# Use with filter() and map()
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
evens = list(filter(lambda x: x % 2 == 0, numbers))
squared = list(map(lambda x: x**2, numbers))

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Classes and OOP

class BankAccount:
    """Bank account class."""
    
    def __init__(self, owner, balance=0):
        self.owner = owner
        self.__balance = balance  # Private attribute (encapsulation)
    
    def deposit(self, amount):
        if amount > 0:
            self.__balance += amount
            print(f"Deposited ${amount:,.2f}. Balance: ${self.__balance:,.2f}")
    
    def withdraw(self, amount):
        if amount > self.__balance:
            print("Insufficient funds!")
        else:
            self.__balance -= amount
            print(f"Withdrew ${amount:,.2f}. Balance: ${self.__balance:,.2f}")
    
    def get_balance(self):
        return self.__balance
    
    def __str__(self):
        return f"{self.owner}'s account (Balance: ${self.__balance:,.2f})"

# Usage
account = BankAccount("Alice", 1000)
account.deposit(500)
account.withdraw(300)
print(account)  # Alice's account (Balance: $1,200.00)

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Inheritance

class SavingsAccount(BankAccount):
    """Savings account that earns interest."""
    
    def __init__(self, owner, balance=0, interest_rate=0.03):
        super().__init__(owner, balance)
        self.interest_rate = interest_rate
    
    def add_interest(self):
        interest = self.get_balance() * self.interest_rate
        self.deposit(interest)
        print(f"Interest added: ${interest:,.2f}")

savings = SavingsAccount("Bob", 5000, 0.05)
savings.add_interest()  # Interest added: $250.00

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