Introduction to Loops

What are Loops?

Loops are a way to repeat code multiple times. Instead of writing the same code over and over, you can use a loop to execute it as many times as needed. Think of a loop like a playlist that repeats your favorite songs!

Why Use Loops?

Loops help you: - Avoid repetition: Write code once, run it many times - Process collections: Work with lists, strings, and other data structures - Automate tasks: Perform actions repeatedly without manual intervention - Save time: Handle large amounts of data efficiently

Real-World Examples

Think about everyday tasks that repeat: - Counting from 1 to 10 - Printing each name in a list - Checking every item in a shopping cart - Sending an email to each person in a contact list

All of these can be done with loops!

Types of Loops in Python

Python has two main types of loops:

1. For loops: Used when you know how many times to repeat (or when iterating over a collection)
2. While loops: Used when you want to repeat until a condition becomes false

A Simple Example

Here's what code looks like without loops:

print("Hello")
print("Hello")
print("Hello")
print("Hello")
print("Hello")

And here's the same thing with a loop:

for i in range(5):
    print("Hello")

Much cleaner! The loop runs 5 times and prints "Hello" each time.

Understanding Loop Structure

Every loop has these parts:

1. Loop keyword: for or while
2. Loop variable: A variable that changes with each iteration
3. Loop body: The code that repeats (indented)
4. Colon: Indicates the start of the loop body

for item in collection:  # Loop header
    print(item)          # Loop body (indented)

The Indentation Rule

In Python, indentation is crucial for loops. The code inside the loop must be indented:

# Correct
for i in range(3):
    print(i)  # This is inside the loop

# Wrong
for i in range(3):
print(i)  # This will cause an error - not indented!

Your First Loop

Let's create a simple loop that counts from 1 to 5:

for number in [1, 2, 3, 4, 5]:
    print(f"Number: {number}")

This will output:

Number: 1
Number: 2
Number: 3
Number: 4
Number: 5

Common Mistakes to Avoid

1. Forgetting the colon: Always include : after the loop header ```python # Wrong for i in range(5) print(i)

# Correct for i in range(5): print(i) ```

1. Wrong indentation: Code inside the loop must be indented ```python # Wrong for i in range(3): print(i)

# Correct for i in range(3): print(i) ```

1. Infinite loops: Be careful with while loops - they can run forever if the condition never becomes false!

Try It Yourself!

Create a loop that prints "Learning Python!" three times:

for i in range(3):
    print("Learning Python!")

What's Next?

Now that you understand what loops are and why they're useful, we'll learn about for loops - the most common type of loop in Python!