Lesson 7: Loops (for, while)

Why Loops Matter

Loops allow your program to repeat actions without writing the same code multiple times. Python provides two main loop types: for loops and while loops.

The for Loop

for loops iterate over sequences such as lists, strings, or ranges.

Looping Through a List

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

Looping Through a Range of Numbers

for i in range(5):
    print(i)
# Output: 0 1 2 3 4

Looping Through a String

for char in "Python":
    print(char)

The while Loop

while loops run as long as a condition is true.

count = 0

while count < 5:
    print(count)
    count += 1

Breaking Out of Loops

Use break to stop a loop early:

for i in range(10):
    if i == 5:
        break
    print(i)

Skipping Iterations

Use continue to skip to the next iteration:

for i in range(5):
    if i == 2:
        continue
    print(i)

Nested Loops

You can place loops inside other loops:

for x in range(3):
    for y in range(2):
        print(x, y)

Looping with else

The else block runs when the loop finishes normally (not interrupted by break):

for i in range(3):
    print(i)
else:
    print("Loop completed.")

Common Loop Pitfalls

• Forgetting to update the condition in a while loop (infinite loop).
• Modifying a list while iterating over it.
• Using range() incorrectly (off‑by‑one errors).

Next Steps

Now that you understand loops, you’re ready to learn how to organize reusable code using functions in Lesson 8: Functions and Parameters.

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