Lesson 6 - Loops (for & while)

Learning Objective

Repeat code with for loops over sequences and ranges, and with while loops driven by a condition; use break and continue to control loop flow.

Introduction

Loops allow you to execute the same block of code multiple times without copying and pasting it.

Python provides two primary loop types:

• for loops — used when iterating over a sequence or a known range of values.
• while loops — used when repetition should continue until a condition becomes false.

Loops are fundamental to programming because they let your programs process collections of data, retry operations, monitor sensors, and automate repetitive tasks.

The for Loop

A for loop iterates over each item in a sequence.

Example:

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

Output:

0
1
2
3
4

The loop automatically stops after the last value.

Using range()

range() generates a sequence of numbers.

range(5)

0, 1, 2, 3, 4

range(2, 6)

2, 3, 4, 5

range(0, 10, 2)

0, 2, 4, 6, 8

Iterating Over Lists

A for loop can iterate directly over items in a list.

fruits = ["apple", "banana", "cherry"]
 
for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

Code

# loops.py
 
# for loop over a range
for i in range(5):
    print(f"Count: {i}")
 
# for loop over a list
fruits = ["apple", "banana", "cherry"]
 
for fruit in fruits:
    print(f"I like {fruit}")
 
# while loop with a counter
countdown = 3
 
while countdown > 0:
    print(f"Launching in {countdown}...")
    countdown -= 1
 
print("Liftoff!")
 
# break and continue
for n in range(10):
    if n == 3:
        continue    # skip this iteration
 
    if n == 6:
        break       # stop the loop entirely
 
    print("n =", n)

Expected Output

Count: 0
Count: 1
Count: 2
Count: 3
Count: 4

I like apple
I like banana
I like cherry

Launching in 3...
Launching in 2...
Launching in 1...
Liftoff!

n = 0
n = 1
n = 2
n = 4
n = 5

The while Loop

A while loop continues running as long as its condition remains true.

Example:

countdown = 3
 
while countdown > 0:
    print(countdown)
    countdown -= 1

Output:

3
2
1

The loop stops when:

countdown > 0

becomes false.

Using continue

The continue statement skips the rest of the current iteration and moves directly to the next one.

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

Output:

0
1
3
4

Notice that 2 is skipped.

Using break

The break statement immediately exits the loop.

for n in range(10):
    if n == 4:
        break
 
    print(n)

Output:

0
1
2
3

The loop stops completely once n becomes 4.

Loop Flow Visualization

for n in range(10):

When:

n == 3

Python executes:

continue

and skips printing.

When:

n == 6

Python executes:

break

and exits the loop immediately.

This is why the output becomes:

0
1
2
4
5

🔧 Under the Hood

range(5)

while condition:

count = 1
 
while count > 0:
    print(count)

count > 0

continue

break

Student Challenge

Challenge 1

Write a FizzBuzz program.

For numbers 1 through 30:

• Print "Fizz" if divisible by 3.
• Print "Buzz" if divisible by 5.
• Print "FizzBuzz" if divisible by both.
• Otherwise print the number itself.

n % 3 == 0

n % 3 == 0 and n % 5 == 0

# fizzbuzz.py
 
for n in range(1, 31):
    if n % 3 == 0 and n % 5 == 0:
        print("FizzBuzz")
    elif n % 3 == 0:
        print("Fizz")
    elif n % 5 == 0:
        print("Buzz")
    else:
        print(n)

Challenge 2

Have your BonicBot hop forward repeatedly, checking for obstacles before every hop.

Experiment with:

max_steps = 10

and:

distance < 0.8

to see how the robot behaves.

Full parameter details for drive_distance() are available in the Python SDK reference.

# challenge_safe_hops.py
 
from bonicbot_bridge import BonicBot
 
with BonicBot(host='192.168.0.188') as bot:
    bot.wait_for_data(timeout=3.0)
 
    step_count = 0
    max_steps = 5
 
    while step_count < max_steps:
        distance = bot.get_min_obstacle_distance()
 
        if distance is not None and distance < 0.5:
            print(f"Obstacle at {distance:.2f} m — stopping.")
            break
 
        print("Path clear, hopping forward.")
        bot.drive_distance(0.2, speed=0.2)
 
        step_count += 1
 
    bot.stop()
    print(f"Stopped after {step_count} hop(s).")

Reflection Question

The while loop above has two ways to stop: break on an obstacle, or step_count reaching max_steps. Why is it safer to have both, rather than relying on the obstacle check alone?