Lesson 7: Lists & Dictionaries

🗂️ Lesson 7: Lists & Dictionaries

⏱️ Estimated time: 35 minutes | Difficulty: Intermediate

Organizing Data

Lists and Dictionaries are the most common ways to store collections of data in Python. One is an ordered list, the other is a set of key-value pairs.

What is a Function?

A function is a reusable block of code. Instead of writing the same code over and over, you create it once and use it many times!

Real-World Analogy:

🎂 Imagine a cookie recipe:
Without functions: You write down the entire recipe every time you want cookies
With functions: You write the recipe once, then just say "Make cookies!" whenever you want them

Creating a Function

def greet():
    print("Hello!")
    print("Welcome!")

Using a Function

def greet():
    print("Hello!")
    print("Welcome!")

# Call the function 3 times
greet()
greet()
greet()

Output:

Hello!
Welcome!
Hello!
Welcome!
Hello!
Welcome!

Functions with Parameters

Parameters are values you pass to a function:

def greet(name):
    print("Hello,", name)
    print("Nice to meet you!")

greet("Alice")
greet("Bob")

Output:

Hello, Alice
Nice to meet you!
Hello, Bob
Nice to meet you!

Functions with Return Values

Use return to send a value back from a function:

def add(a, b):
    result = a + b
    return result

answer = add(5, 3)
print(answer)
print(add(10, 20))

Output:

8
30

Multiple Parameters

def calculate_price(quantity, price_per_item):
    total = quantity * price_per_item
    return total

cost = calculate_price(5, 10)
print("Total cost:", cost)

Output:

Total cost: 50