Lesson 14: Python While Loops, For Loops, and the `range()` Function

Lesson Introduction

Welcome to Lesson 14! Today we are going to learn one of the most powerful ideas in programming: loops.

Imagine you are at the Balogun Market in Lagos and you need to count every customer who enters the shop. Would you write a separate line of code for each customer? No — that would take forever! Instead, you use a loop: a tool that tells Python to repeat a set of instructions automatically.

Python has two types of loops:

The while loop — keeps repeating as long as a condition is true
The for loop — repeats once for each item in a sequence (like a list, string, or range of numbers)

We will also learn about the range() function, which is Python’s built-in tool for generating sequences of numbers. It works hand-in-hand with loops and is used everywhere in real Python code.

What You Will Learn in This Lesson

By the end of this lesson, you will be able to:

Explain what a loop is and why it is useful
Write a while loop with a proper condition and counter
Use break and continue to control loop behaviour
Add an else block to both while and for loops
Write a for loop that iterates over lists, strings, and ranges of numbers
Use range() with one, two, or three arguments
Loop through a string character by character
Write nested loops (a loop inside a loop)
Use the pass statement inside an empty loop
Convert a range to a list and slice it
Test membership in a range using in
Use len() to get the number of elements in a range
Build a practical mini-project using all three tools

Prerequisite Concepts

Before we continue, let us quickly review ideas you have already learned. These concepts will appear throughout this lesson.

Variables and Assignment

A variable stores a value. You set it with =.

i = 1       # i is a variable holding the integer 1
name = "Adaeze"

Conditions and Comparison Operators

A condition is a question that Python answers with True or False. You already know these from the if statement lesson.

Operator	Meaning	Example	Result
`<`	Less than	`3 < 6`	`True`
`>`	Greater than	`7 > 10`	`False`
`==`	Equal to	`5 == 5`	`True`
`!=`	Not equal to	`4 != 4`	`False`
`<=`	Less than or equal	`6 <= 6`	`True`
`>=`	Greater than or equal	`8 >= 9`	`False`

The `print()` Function

You use print() to display a value or message on the screen.

print("Good morning Lagos!")
print(42)

Lists

A list is an ordered collection of items.

foods = ["jollof rice", "egusi soup", "suya"]

You already know all of this. Now let us put it to work inside loops!

Section 1: What Is a Loop?

Why Does a Loop Exist?

Imagine Emeka is a teacher at a secondary school in Abuja. He wants to print the name of every student in his class. The class has 30 students. Without a loop, he would have to write 30 separate print() lines. That is tedious, error-prone, and wastes time.

A loop is an instruction that tells Python:

“Run this block of code repeatedly. Keep going until I tell you to stop.”

This is the core idea. Everything else in this lesson builds on top of it.

Section 2: The `while` Loop

What Is a `while` Loop?

A while loop checks a condition before every repetition. As long as the condition is True, the loop body keeps running. The moment the condition becomes False, the loop stops.

Think of it like a security guard at a Lagos bank: “While the queue has customers, keep serving the next person.”

The Syntax (Structure)

while condition:
    # code to repeat

while — the keyword that starts the loop
condition — any True/False expression (just like in an if statement)
: — the colon that opens the loop body
indented code — the instructions that run on every repetition

Simple Example 1: Count from 1 to 5

i = 1
while i < 6:
    print(i)
    i += 1

Expected Output:

Let us go line by line:

i = 1 — We create a variable i and start it at 1. This is called the counter variable or loop variable.
while i < 6: — Python checks: “Is i less than 6?” If yes, enter the loop. If no, skip it entirely.
print(i) — Print the current value of i.
i += 1 — This means i = i + 1. We increase i by 1. This is called incrementing the counter.
After i += 1, Python goes back to while i < 6: and checks the condition again.
When i reaches 6, the condition i < 6 becomes False, and the loop ends.

Very Important: You must update the counter variable inside the loop (i += 1). If you forget, i stays at 1 forever, and the condition i < 6 is always True. This creates an infinite loop — a loop that never stops. Your program will freeze!

Simple Example 2: Countdown from 5 to 1

Let us count down this time:

i = 5
while i > 0:
    print(i)
    i -= 1   # i -= 1 means i = i - 1 (decrement)
print("Liftoff!")

Expected Output:

5
4
3
2
1
Liftoff!

Notice: the print("Liftoff!") line is not indented, so it runs after the loop finishes.

💡 Thinking Prompt: What happens if you change i = 5 to i = 3? How many times will the loop run?

Section 3: Controlling `while` Loops — `break`, `continue`, and `else`

3.1 The `break` Statement

The break keyword immediately exits the loop — even if the condition is still True. It is like an emergency exit.

Real-life analogy: Imagine Ngozi is sampling bottles of groundnut oil in a warehouse. She checks each bottle. The moment she finds a bad one, she breaks — she stops checking and reports the problem immediately.

Example: Stop the loop when `i` equals 3

i = 1
while i < 6:
    print(i)
    if i == 3:
        break
    i += 1

Expected Output:

1
2
3

Line-by-line explanation:

The loop starts with i = 1 and counts up.
On each repetition, it prints i, then checks if i == 3.
When i becomes 3, Python hits break and immediately exits the loop.
The numbers 4 and 5 are never printed.

⚠️ Notice that i += 1 is after the if check. So when i is 3, Python prints 3, then hits break, and never reaches i += 1.

3.2 The `continue` Statement

The continue keyword skips the rest of the current repetition and jumps back to check the condition again. It does not exit the loop — it just skips one turn.

Real-life analogy: Amaka is reading through 10 exam papers. Whenever she sees a blank paper, she continues — she skips it and moves on to the next one, without stopping the whole process.

Example: Skip number 3, print everything else from 1 to 5

i = 0
while i < 6:
    i += 1
    if i == 3:
        continue
    print(i)

Expected Output:

Careful study of this code:

i = 0 — We start at 0 this time.
i += 1 — This is the first line inside the loop. It increments i before anything else.
if i == 3: continue — When i is 3, Python jumps back to while i < 6: without reaching print(i).
All other values of i reach print(i) and get printed.

🔑 Why does i += 1 come before the if check here? Because if i += 1 were after continue, we would never increment i when i == 3. That would create an infinite loop! Always plan where your increment goes.

3.3 The `else` Statement in a `while` Loop

Python allows you to attach an else block to a while loop. The else block runs once — right after the loop condition becomes False (i.e., when the loop ends naturally).

Important rule: The else block does NOT run if the loop ends with break.

Example: Count from 1 to 5, then announce the end

i = 1
while i < 6:
    print(i)
    i += 1
else:
    print("i is no longer less than 6")

Expected Output:

1
2
3
4
5
i is no longer less than 6

Example: The `else` block does NOT run after `break`

i = 1
while i < 6:
    print(i)
    if i == 3:
        break
    i += 1
else:
    print("This will NOT print because break was used!")

Expected Output:

1
2
3

The else block is skipped entirely because break ended the loop.

💡 Real-world use: The while-else pattern is great for search tasks. Loop while searching; if found, break. The else block runs only if you finished searching without finding it — which means “not found.”

Section 4: The `for` Loop

What Is a `for` Loop?

A for loop is used to iterate over a sequence. “Iterate” means to go through each item, one by one.

Think of it like Fatimah checking every stall at a market. She visits each stall — no more, no less — and does something at each one.

A for loop works on:

Lists
Tuples
Strings (every character is treated as a single item)
Dictionaries
Sets
Ranges (we will cover this soon)

The key difference from while: A for loop does not need you to manage a counter variable manually. Python automatically picks up the next item from the sequence on each turn.

The Syntax

for variable in sequence:
    # code to run for each item

for — keyword that starts the loop
variable — a name you choose; Python puts the current item here on each turn
in — keyword connecting the variable to the sequence
sequence — the list, string, or range to loop through
: — opens the loop body
indented code — runs once for every item

Simple Example 1: Loop through a list of Nigerian foods

foods = ["jollof rice", "egusi soup", "suya", "puff puff"]
for food in foods:
    print(food)

Expected Output:

jollof rice
egusi soup
suya
puff puff

What is happening here?

On Turn 1: Python sets food = "jollof rice" and runs print(food).
On Turn 2: Python sets food = "egusi soup" and runs print(food).
This continues until every item in the list has been visited.
The loop ends automatically. No i += 1 needed!

Simple Example 2: Loop through names

names = ["Chidi", "Aisha", "Emeka", "Ngozi"]
for name in names:
    print("Hello,", name)

Expected Output:

Hello, Chidi
Hello, Aisha
Hello, Emeka
Hello, Ngozi

Section 5: Looping Through a String

Strings are sequences of characters, so you can loop through them letter by letter.

Example: Print each letter in a city name

for letter in "Lagos":
    print(letter)

Expected Output:

L
a
g
o
s

On each turn, letter holds the next character in the string "Lagos". After the last character "s", the loop ends.

Example: Count vowels in a word

word = "Abuja"
vowels = "aeiouAEIOU"
count = 0

for letter in word:
    if letter in vowels:
        count += 1

print("Number of vowels:", count)

Expected Output:

Number of vowels: 3

(The vowels in “Abuja” are: A, u, a)

💡 Thinking Prompt: What would happen if you change "Abuja" to "Kano"? How many vowels does “Kano” have? Try to predict before running the code.

Section 6: `break` and `continue` in `for` Loops

Just like in while loops, you can use break and continue inside for loops.

6.1 `break` in a `for` Loop

break exits the loop immediately when a condition is met.

Example 1: Stop when you find “banana”

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

Expected Output:

apple
banana

The loop prints "apple", then "banana", then hits break and stops. "cherry" is never printed.

Example 2: Break BEFORE printing

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

Expected Output:

apple

Here, the if check comes before print. So when fruit == "banana", Python breaks before ever printing "banana".

💡 Thinking Prompt: Why does Example 1 print “banana” but Example 2 does not? What changed?

6.2 `continue` in a `for` Loop

continue skips the current item and moves to the next one.

Example: Print all fruits except “banana”

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

Expected Output:

apple
cherry

When fruit == "banana", Python hits continue, skips print(fruit), and immediately goes to the next item in the list — which is "cherry".

Section 7: The `range()` Function

Why Does `range()` Exist?

Imagine you want to print the numbers from 1 to 1000. You definitely do not want to type out a list of 1000 numbers! The range() function solves this: it generates a sequence of numbers automatically.

What is range()? range() is a built-in Python function that returns an immutable sequence of numbers. “Immutable” means the sequence cannot be changed after it is created. It has its own special data type, also called range.

The Syntax

range(start, stop, step)

Parameter	What it means	Is it required?	Default value
`start`	The first number in the sequence	Optional	`0`
`stop`	The sequence ends before this number	Required	—
`step`	How much to add each time	Optional	`1`

7.1 `range()` with One Argument

When you call range() with only one number, that number is the stop value. The sequence starts at 0 and goes up to but not including the stop value.

x = range(10)
print(list(x))

Expected Output:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

⚠️ range(10) gives you numbers 0 to 9, not 0 to 10! The stop value is exclusive — it is not included.

💡 Tip: To display the contents of a range, we wrap it in list(). This converts it to a regular list that print() can show. You will learn more about this below.

7.2 `range()` with Two Arguments

When you call range() with two numbers, the first is start and the second is stop.

x = range(3, 10)
print(list(x))

Expected Output:

[3, 4, 5, 6, 7, 8, 9]

The sequence starts at 3 and goes up to 9 (not 10).

7.3 `range()` with Three Arguments

When you call range() with three numbers, the third is the step — how much to add each time.

x = range(2, 30, 3)
print(list(x))

Expected Output:

[2, 5, 8, 11, 14, 17, 20, 23, 26, 29]

Starting at 2, add 3 each time, stop before 30.

7.4 Using `range()` in a `for` Loop

This is the most common use of range(): to run a loop a specific number of times.

Example 1: Print numbers 0 to 5

for x in range(6):
    print(x)

Expected Output:

Example 2: Print numbers 2 to 5 (using start and stop)

for x in range(2, 6):
    print(x)

Expected Output:

Example 3: Print even numbers from 0 to 20 (using step)

for x in range(0, 21, 2):
    print(x)

Expected Output:

Example 4: Count down using a negative step

for x in range(10, 0, -1):
    print(x)

Expected Output:

When the step is negative, the sequence counts down. Start must be greater than stop for this to work.

Section 8: Advanced `range()` — Converting, Slicing, Membership, and Length

8.1 Converting a `range` to a List

The range object itself is not a list — it just represents the numbers. To display all the values at once, convert it to a list using list().

print(list(range(5)))
print(list(range(1, 6)))
print(list(range(5, 20, 3)))

Expected Output:

[0, 1, 2, 3, 4]
[1, 2, 3, 4, 5]
[5, 8, 11, 14, 17]

8.2 Slicing a `range`

You can access individual elements of a range using index notation (just like a list), and you can also slice it.

r = range(10)
print(r[2])     # the item at index 2
print(r[:3])    # a new range from index 0 up to (not including) 3

Expected Output:

2
range(0, 3)

r[2] gives you the value at position 2, which is 2 (since the range starts at 0).
r[:3] gives you a new range object — range(0, 3) — not a list.

8.3 Testing Membership with `in`

You can check whether a number is inside a range using the in operator.

r = range(0, 10, 2)
print(list(r))
print(6 in r)
print(7 in r)

Expected Output:

[0, 2, 4, 6, 8]
True
False

6 in r is True because 6 is in the sequence [0, 2, 4, 6, 8].
7 in r is False because 7 is not in that sequence (we skip odd numbers with step 2).

8.4 Getting the Length of a `range`

Use len() to find out how many numbers are in a range.

r = range(0, 10, 2)
print(len(r))

Expected Output:

The range [0, 2, 4, 6, 8] has 5 numbers, so len(r) returns 5.

Section 9: `else` in a `for` Loop

Just like with while, you can add an else block to a for loop. It runs once after the loop has finished iterating through all items — but only if the loop was not ended by a break.

Example 1: Normal completion — `else` runs

for x in range(6):
    print(x)
else:
    print("Finally finished!")

Expected Output:

0
1
2
3
4
5
Finally finished!

Example 2: Loop broken early — `else` does NOT run

for x in range(6):
    if x == 3:
        break
    print(x)
else:
    print("Finally finished!")

Expected Output:

0
1
2

The else block is skipped because break ended the loop at x == 3.

💡 Real-world use: This pattern is common in search tasks. You loop through a list looking for something. If you find it, you break. The else block runs only if you went through the entire list and never found it.

Section 10: Nested Loops

A nested loop is a loop inside another loop. The inner loop runs completely for every single step of the outer loop.

Real-life analogy: Think of Damilola visiting every floor of a building in Lagos, and on each floor she knocks on every office door. For each floor (outer loop), she knocks on every door (inner loop).

The Syntax

for outer_item in outer_sequence:
    for inner_item in inner_sequence:
        # this code runs for every combination

Example 1: Print combinations of colours and items

colours = ["red", "green", "blue"]
items = ["bag", "shoe"]

for colour in colours:
    for item in items:
        print(colour, item)

Expected Output:

red bag
red shoe
green bag
green shoe
blue bag
blue shoe

For every colour (3 colours), Python goes through all items (2 items). Total combinations: 3 × 2 = 6 lines.

Example 2: Multiplication table for 3 using nested loops

for i in range(1, 4):        # outer loop: i goes 1, 2, 3
    for j in range(1, 6):    # inner loop: j goes 1, 2, 3, 4, 5
        print(i, "x", j, "=", i * j)
    print("---")             # printed after each inner loop finishes

Expected Output:

x 1 = 1
x 2 = 2
x 3 = 3
x 4 = 4
x 5 = 5
---
x 1 = 2
x 2 = 4
x 3 = 6
x 4 = 8
x 5 = 10
---
x 1 = 3
x 2 = 6
x 3 = 9
x 4 = 12
x 5 = 15
---

Section 11: The `pass` Statement in Loops

A for loop (or while loop) cannot be empty. If you write a loop with no body, Python will give you a SyntaxError. But sometimes, while you are planning your code, you want to create a loop body you have not written yet. The pass statement acts as a placeholder.

for x in [0, 1, 2]:
    pass

This runs without any output and without any errors. pass tells Python: “There is nothing to do here — just continue.”

💡 This is useful when you are building a program in stages. You sketch out the loop first with pass, then come back to fill in the body later.

Guided Practice Exercises

Exercise 1: The Patient Bus Driver

Scenario: Alhaji Musa drives a danfo bus on the Lagos–Ibadan expressway. He wants to track how many trips he has made. He will keep driving until he completes 5 trips.

Objective: Use a while loop to simulate 5 bus trips.

Steps:

Create a variable trips = 0
Write a while loop that runs as long as trips < 5
Inside the loop, print the current trip number, then increment trips
After the loop, print “All trips complete!”

Expected Output:

Trip 1 in progress...
Trip 2 in progress...
Trip 3 in progress...
Trip 4 in progress...
Trip 5 in progress...
All trips complete!

Solution:

trips = 0
while trips < 5:
    trips += 1
    print("Trip", trips, "in progress...")
else:
    print("All trips complete!")

Self-check:

Did the loop run exactly 5 times?
What would happen if you changed the condition to trips < 10?
Did the else block print at the end?

Exercise 2: Market Price Checker

Scenario: Adaeze is at Wuse Market in Abuja checking prices of vegetables. She has a list of prices in Naira. She wants to print each price, but skip any price that is exactly 500 (she thinks it is a pricing error).

Objective: Use a for loop with continue to skip a specific value.

Steps:

Create a list: prices = [200, 350, 500, 420, 180, 500, 650]
Write a for loop over prices
If the current price is 500, use continue to skip it
Otherwise, print the price

Expected Output:

Solution:

prices = [200, 350, 500, 420, 180, 500, 650]

for price in prices:
    if price == 500:
        continue
    print(price)

What-if challenge: Change continue to break. What happens? Why?

Exercise 3: Finding a Ripe Mango

Scenario: Chukwuemeka is checking a crate of mangoes to find the first ripe one. Once he finds it, he stops — he does not need to check the rest.

Objective: Use a for loop with break and the for-else pattern.

Steps:

Create a list: mangoes = ["unripe", "unripe", "ripe", "unripe", "ripe"]
Write a for loop over mangoes with an index using range(len(mangoes))
Print which position is being checked
If the mango is “ripe”, print a success message and break
Add an else block that runs only if no ripe mango was found

Solution:

mangoes = ["unripe", "unripe", "ripe", "unripe", "ripe"]

for i in range(len(mangoes)):
    print("Checking mango at position", i)
    if mangoes[i] == "ripe":
        print("Found a ripe mango at position", i, "!")
        break
else:
    print("No ripe mango found in this crate.")

Expected Output:

Checking mango at position 0
Checking mango at position 1
Checking mango at position 2
Found a ripe mango at position 2 !

What-if challenge: Change all mangoes to “unripe”. Does the else block run now?

Mini Project: Nigerian JAMB Score Analyser

In this project, you will build a simple tool that analyses JAMB exam scores for a group of students. You will use for loops, range(), if statements, and loops with break.

Stage 1: Setup — Define the Student Scores

students = [
    ("Emeka", 280),
    ("Aisha", 195),
    ("Chioma", 315),
    ("Tunde", 150),
    ("Ngozi", 260),
    ("Yusuf", 330)
]

Each item is a tuple containing a name and a score.

Expected Output: (nothing yet — we are setting up)

Stage 2: Print All Scores

Use a for loop to print every student’s name and score.

print("=== JAMB Results ===")
for name, score in students:
    print(name, "->", score)

Expected Output:

=== JAMB Results ===
Emeka -> 280
Aisha -> 195
Chioma -> 315
Tunde -> 150
Ngozi -> 260
Yusuf -> 330

Stage 3: Classify Each Score

Add a grade classification based on the score.

print("\n=== Score Classification ===")
for name, score in students:
    if score >= 300:
        grade = "Excellent"
    elif score >= 250:
        grade = "Good"
    elif score >= 200:
        grade = "Pass"
    else:
        grade = "Below Cut-off"
    print(name, ":", score, "->", grade)

Expected Output:

=== Score Classification ===
Emeka : 280 -> Good
Aisha : 195 -> Below Cut-off
Chioma : 315 -> Excellent
Tunde : 150 -> Below Cut-off
Ngozi : 260 -> Good
Yusuf : 330 -> Excellent

Stage 4: Calculate the Average Score

Use a for loop and range() to compute the average.

total = 0
for name, score in students:
    total += score

average = total / len(students)
print("\nAverage Score:", average)

Expected Output:

Average Score: 255.0

Stage 5: Find the Top Scorer

Loop through the students and track the highest score.

top_name = ""
top_score = 0

for name, score in students:
    if score > top_score:
        top_score = score
        top_name = name

print("\nTop Scorer:", top_name, "with", top_score, "points")

Expected Output:

Top Scorer: Yusuf with 330 points

Stage 6: Count Students Above Cut-off (using `range()`)

cutoff = 200
above_cutoff = 0

for i in range(len(students)):
    name, score = students[i]
    if score >= cutoff:
        above_cutoff += 1

print("\nStudents above cut-off of", cutoff, ":", above_cutoff)

Expected Output:

Students above cut-off of 200 : 4

Final Combined Output

=== JAMB Results ===
Emeka -> 280
Aisha -> 195
Chioma -> 315
Tunde -> 150
Ngozi -> 260
Yusuf -> 330

=== Score Classification ===
Emeka : 280 -> Good
Aisha : 195 -> Below Cut-off
Chioma : 315 -> Excellent
Tunde : 150 -> Below Cut-off
Ngozi : 260 -> Good
Yusuf : 330 -> Excellent

Average Score: 255.0

Top Scorer: Yusuf with 330 points

Students above cut-off of 200 : 4

Extension Challenges:

Add a loop that counts how many students scored “Excellent”.
Use a while loop to let the user keep entering student names until they type “done”.
Use range(len(students) - 1, -1, -1) to print the results in reverse order.

Common Beginner Mistakes

Mistake 1: Forgetting to Increment in a `while` Loop

# WRONG — infinite loop!
i = 1
while i < 6:
    print(i)
    # i never changes! i stays at 1 forever

# CORRECT
i = 1
while i < 6:
    print(i)
    i += 1   # always update the counter!

How to spot it: Your program prints the same number over and over and never stops. Press Ctrl + C to force-quit.

Mistake 2: Off-by-One Error with `range()`

# WRONG — only prints 1 to 4, not 1 to 5
for i in range(1, 5):
    print(i)

# CORRECT — to include 5, stop must be 6
for i in range(1, 6):
    print(i)

Rule to remember: range(start, stop) includes start but excludes stop. If you want to include a number n, write range(1, n + 1).

Mistake 3: Wrong Indentation in Loop Body

# WRONG — the print is outside the loop!
for i in range(3):
    pass
print(i)   # this only runs once, after the loop

# CORRECT — print is inside the loop
for i in range(3):
    print(i)   # this runs 3 times

In Python, indentation is everything. The loop body must be indented (4 spaces or 1 tab) consistently.

Mistake 4: Expecting `continue` to Exit the Loop

# WRONG thinking — continue does NOT exit the loop
for i in range(5):
    if i == 3:
        continue   # this SKIPS 3, but the loop keeps going
    print(i)

# If you want to EXIT at 3, use break:
for i in range(5):
    if i == 3:
        break
    print(i)

Mistake 5: Confusing `range(n)` with a List

# WRONG — range is not a list; you cannot do this directly
r = range(5)
print(r)   # Output: range(0, 5) — NOT [0, 1, 2, 3, 4]

# CORRECT — convert to a list to see all values
print(list(r))   # Output: [0, 1, 2, 3, 4]

Mistake 6: Empty `for` Loop Body

# WRONG — this causes a SyntaxError
for x in range(5):
    # nothing here

# CORRECT — use pass as a placeholder
for x in range(5):
    pass

Mistake 7: Expecting `else` to Run After `break`

# WRONG expectation
for x in range(5):
    if x == 3:
        break
else:
    print("This runs!")   # This does NOT run after break

# The else block only runs if the loop completed WITHOUT break

Reflection Questions

Take a moment to think through these questions. Try to answer them in your own words before checking your notes.

What is the key difference between a while loop and a for loop?
In a while loop, what happens if you forget to increment the counter variable?
What does break do? How is it different from continue?
What does range(3, 15, 3) produce? List the numbers without running the code.
Why does range(10) give you numbers 0–9 and not 1–10?
When does the else block in a loop run? When does it NOT run?
In a nested loop, how many times does the inner loop run in total if the outer loop runs 4 times and the inner loop runs 3 times each?
What is the purpose of the pass statement inside a loop?
How do you check if the number 15 is in range(0, 30, 5) without converting it to a list?
Why is range() more efficient than writing out a full list of numbers?

Completion Checklist

Before moving to the next lesson, confirm you can do all of these:

Lesson Summary

Congratulations! You have just mastered Python’s three fundamental looping tools. Here is a recap of everything we covered:

while loops repeat a block of code as long as a condition is True. They require you to manage a counter variable manually. Always remember to increment the counter to avoid an infinite loop.

break immediately exits any loop. continue skips the current iteration and jumps to the next. Both work in while and for loops.

else in loops runs once after the loop ends naturally, but is skipped if break was used. This is useful for “not found” scenarios.

for loops iterate over every item in a sequence (lists, strings, tuples, ranges) without needing a manual counter. Python handles the stepping automatically.

range() generates sequences of numbers. It takes 1, 2, or 3 arguments (start, stop, step). The stop value is always excluded. It supports indexing, slicing, membership testing with in, and length with len().

Nested loops are loops inside loops. The inner loop completes fully for each step of the outer loop.

pass is a placeholder for an empty loop body, preventing SyntaxError.

Quick-Reference Card

Feature	Syntax	Notes
`while` loop	`while condition:`	Runs while condition is `True`; needs manual counter
`for` loop	`for item in sequence:`	Iterates over every item automatically
`break`	`break`	Immediately exits the loop
`continue`	`continue`	Skips current iteration; continues to next
Loop `else`	`else:` after loop	Runs after loop ends, NOT after `break`
`range(n)`	`range(5)` → `0,1,2,3,4`	One argument: stop only; starts at 0
`range(a, b)`	`range(2, 6)` → `2,3,4,5`	Two arguments: start and stop
`range(a, b, s)`	`range(0, 10, 2)` → `0,2,4,6,8`	Three arguments: start, stop, step
Negative step	`range(5, 0, -1)` → `5,4,3,2,1`	Counts downward
Convert range	`list(range(5))`	Shows all values in the range
Test membership	`7 in range(0, 10, 2)` → `False`	Checks if a number is in the range
Range length	`len(range(0, 10, 2))` → `5`	Count of numbers in the range
Nested loops	`for x in ...: for y in ...:`	Inner loop runs fully for each outer iteration
`pass`	`pass`	Placeholder for empty loop body

End of Lesson 14 — Next up: Python Functions

Lesson 14: Python While Loops, For Loops, and the range() Function

Lesson Introduction

What You Will Learn in This Lesson

Prerequisite Concepts

Variables and Assignment

Conditions and Comparison Operators

The print() Function

Lists

Section 1: What Is a Loop?

Why Does a Loop Exist?

Section 2: The while Loop

What Is a while Loop?

The Syntax (Structure)

Simple Example 1: Count from 1 to 5

Simple Example 2: Countdown from 5 to 1

Section 3: Controlling while Loops — break, continue, and else

3.1 The break Statement

Example: Stop the loop when i equals 3

3.2 The continue Statement

Example: Skip number 3, print everything else from 1 to 5

3.3 The else Statement in a while Loop

Example: Count from 1 to 5, then announce the end

Example: The else block does NOT run after break

Section 4: The for Loop

What Is a for Loop?

The Syntax

Simple Example 1: Loop through a list of Nigerian foods

Simple Example 2: Loop through names

Section 5: Looping Through a String

Example: Print each letter in a city name

Example: Count vowels in a word

Section 6: break and continue in for Loops

6.1 break in a for Loop

Example 1: Stop when you find “banana”

Example 2: Break BEFORE printing

6.2 continue in a for Loop

Example: Print all fruits except “banana”

Section 7: The range() Function

Why Does range() Exist?

The Syntax

7.1 range() with One Argument

7.2 range() with Two Arguments

7.3 range() with Three Arguments

7.4 Using range() in a for Loop

Example 1: Print numbers 0 to 5

Example 2: Print numbers 2 to 5 (using start and stop)

Example 3: Print even numbers from 0 to 20 (using step)

Example 4: Count down using a negative step

Section 8: Advanced range() — Converting, Slicing, Membership, and Length

8.1 Converting a range to a List

8.2 Slicing a range

8.3 Testing Membership with in

8.4 Getting the Length of a range

Section 9: else in a for Loop

Example 1: Normal completion — else runs

Example 2: Loop broken early — else does NOT run

Section 10: Nested Loops

The Syntax

Example 1: Print combinations of colours and items

Example 2: Multiplication table for 3 using nested loops

Section 11: The pass Statement in Loops

Guided Practice Exercises

Exercise 1: The Patient Bus Driver

Exercise 2: Market Price Checker

Exercise 3: Finding a Ripe Mango

Mini Project: Nigerian JAMB Score Analyser

Stage 1: Setup — Define the Student Scores

Stage 2: Print All Scores

Stage 3: Classify Each Score

Stage 4: Calculate the Average Score

Stage 5: Find the Top Scorer

Stage 6: Count Students Above Cut-off (using range())

Final Combined Output

Common Beginner Mistakes

Mistake 1: Forgetting to Increment in a while Loop

Mistake 2: Off-by-One Error with range()

Mistake 3: Wrong Indentation in Loop Body

Mistake 4: Expecting continue to Exit the Loop

Mistake 5: Confusing range(n) with a List

Mistake 6: Empty for Loop Body

Lesson 14: Python While Loops, For Loops, and the `range()` Function

The `print()` Function

Section 2: The `while` Loop

What Is a `while` Loop?

Section 3: Controlling `while` Loops — `break`, `continue`, and `else`

3.1 The `break` Statement

Example: Stop the loop when `i` equals 3

3.2 The `continue` Statement

3.3 The `else` Statement in a `while` Loop

Example: The `else` block does NOT run after `break`

Section 4: The `for` Loop

What Is a `for` Loop?

Section 6: `break` and `continue` in `for` Loops

6.1 `break` in a `for` Loop

6.2 `continue` in a `for` Loop

Section 7: The `range()` Function

Why Does `range()` Exist?

7.1 `range()` with One Argument

7.2 `range()` with Two Arguments

7.3 `range()` with Three Arguments

7.4 Using `range()` in a `for` Loop

Section 8: Advanced `range()` — Converting, Slicing, Membership, and Length

8.1 Converting a `range` to a List

8.2 Slicing a `range`

8.3 Testing Membership with `in`

8.4 Getting the Length of a `range`

Section 9: `else` in a `for` Loop

Example 1: Normal completion — `else` runs

Example 2: Loop broken early — `else` does NOT run

Section 11: The `pass` Statement in Loops

Stage 6: Count Students Above Cut-off (using `range()`)

Mistake 1: Forgetting to Increment in a `while` Loop

Mistake 2: Off-by-One Error with `range()`

Mistake 4: Expecting `continue` to Exit the Loop

Mistake 5: Confusing `range(n)` with a List

Mistake 6: Empty `for` Loop Body

Mistake 7: Expecting `else` to Run After `break`