LESSON 15 · PRACTICE PROJECT20 min

Project: Number Guessing Game

Use comparisons, a function, and a loop to evaluate guesses until the answer is found.

VIDEO LESSON

Video coming to YouTube

Work through the full lesson and run its code while the video is being prepared for publication.

THE IDEA

Understand the concept

A guessing game needs three outcomes. A guess below the secret number is too low; one above it is too high; an equal guess is correct. A function can return the matching message, making the decision easy to test.

The starter runs a prepared list of guesses so the result is repeatable in the browser. The loop prints each attempt and stops with break when the function returns Correct. After the checked task, you can change the list or replace it with input() for interactive play.

Keeping the secret fixed while learning makes debugging easier. A later variation can choose a random secret, but then an example's exact output depends on the random result.

Compare with <, >, and ==
Return one of three outcomes
break exits a loop after a correct guess

WORKED EXAMPLES

See it step by step

Read the code, predict the output, then compare it with the result.

01. Compare a guess

PYTHON

secret = 5
guess = 2
if guess < secret:
    print("Too low")

EXPECTED OUTPUT

Too low

The condition is true because 2 is less than 5.

02. Stop after a match

PYTHON

for guess in [2, 5, 9]:
    print(guess)
    if guess == 5:
        break

EXPECTED OUTPUT

2
5

The loop prints 2 and 5, then break prevents the later guess of 9.

03. Number attempts

PYTHON

for number, guess in enumerate([3, 7], start=1):
    print(number, guess)

EXPECTED OUTPUT

1 3
2 7

enumerate pairs each item with a count beginning at one.

GO DEEPER

A closer look

Follow the reasoning, inspect each result, then try the suggested changes in the console below.

01 / 03

Model the game as changing state

A game is easier to reason about when you list the facts that can change: the secret stays fixed, the current guess changes, and the attempt count increases. The game ends when the guess matches the secret or when the attempt limit is reached. A function that evaluates one guess and a loop that controls the whole game have different jobs. Keeping them separate lets you check the decision rules without playing an entire game.

The browser lesson uses prepared guesses to make the output repeatable. The same loop could later receive guesses from a human, but input() would wait for input and is awkward for an automatically checked example. Trace the list below by hand: which guesses are visited, what is the attempt count at each one, and why is the last item never printed?

PYTHON

secret = 6
guesses = [2, 8, 6, 4]
for attempt, guess in enumerate(guesses, start=1):
    if guess == secret:
        print(f"Attempt {attempt}: win")
        break
    print(f"Attempt {attempt}: keep trying")

EXPECTED OUTPUT

Attempt 1: keep trying
Attempt 2: keep trying
Attempt 3: win

Follow the reasoning

enumerate pairs each prepared guess with its one-based attempt number.
The equality branch prints the win and exits before guess 4.
Move 6 to the first position and predict the number of printed lines.

02 / 03

Use hints to narrow the search

A low or high hint is information about an entire interval, not just one guess. If the secret is between 1 and 20 and 4 is too low, every number from 1 through 4 is ruled out. If 14 is too high, every number from 14 through 20 is ruled out. Keeping lower and upper bounds makes this reasoning visible to the player.

The bounds here are inclusive. After a low guess, the new minimum is guess + 1; after a high guess, the new maximum is guess - 1. Forgetting the plus or minus one leaves a value that has already been rejected in the range. With a real player, you could display the updated interval after each turn.

PYTHON

low, high = 1, 20
secret = 10
for guess in [4, 14, 10]:
    if guess < secret:
        low = guess + 1
        print(f"Try {low} through {high}")
    elif guess > secret:
        high = guess - 1
        print(f"Try {low} through {high}")
    else:
        print("Found it")
        break

EXPECTED OUTPUT

Try 5 through 20
Try 5 through 13
Found it

Follow the reasoning

Guess 4 excludes 1–4; guess 14 then excludes 14–20.
The equality branch ends the loop without changing either bound.
Replace the second guess with 8 and predict the new interval.

03 / 03

Keep bad entries from costing a turn

Human input arrives as text, even when a person intended a number. int('five') raises ValueError, and a number outside the game range should also be rejected. Decide whether an invalid entry counts as an attempt before you write the loop. In this example, invalid entries are reported but do not increase the count. That policy makes the attempt limit fair and testable.

Separating parsing from the game rule prevents a bad entry from reaching the comparison logic. The sample uses a fixed list of strings so you can run it without an input prompt. A full game could repeatedly ask for text, parse it, and only then spend an attempt. The same approach applies to forms and command-line tools.

PYTHON

entries = ["five", "0", "7"]
attempts = 0
for entry in entries:
    try:
        guess = int(entry)
    except ValueError:
        print("Enter a whole number")
        continue
    if not 1 <= guess <= 10:
        print("Choose 1 to 10")
        continue
    attempts += 1
    print(f"Valid attempt {attempts}: {guess}")

EXPECTED OUTPUT

Enter a whole number
Choose 1 to 10
Valid attempt 1: 7

Follow the reasoning

continue skips the attempt counter for text and out-of-range values.
Only the valid 7 is counted as an attempt.
Add '11' to entries and predict whether the count changes.

HANDS-ON

Try it in Python

Edit the example and run it. Python starts in your browser the first time you click Run.

Python console

Ready to run

def check_guess(secret, guess):
    # Return "Too low", "Too high", or "Correct".
    return "Keep trying"

secret = 7
guesses = [3, 9, 7, 8]
for attempt, guess in enumerate(guesses, start=1):
    result = check_guess(secret, guess)
    print(f"Attempt {attempt}: {result}")
    if result == "Correct":
        break

Need input()? Add one value per line

Input lines

Ctrl / ⌘ + Enter to run

OUTPUT

Your output appears here.

Your turnFinish check_guess(secret, guess) so it returns exactly Too low, Too high, or Correct. Run the prepared guesses and make the final line Attempt 3: Correct. The game should stop after a correct answer.

Need a hint?

Use if guess < secret, elif guess > secret, and else. Return the specified strings without extra punctuation. The existing loop already stops on Correct.

Complete the task and select Check task to verify your code.

DEBUG BETTER

Typical mistakes

Everyone meets these errors. See what causes them and how to fix them.

Assigning instead of comparing

COMMON MISTAKE

if guess = secret:
    print('Correct')

FIX

if guess == secret:
    print('Correct')

What happens: SyntaxError because = is assignment, not comparison.
Use == when asking whether two values are equal.

Reversing the low hint

COMMON MISTAKE

if guess < secret:
    return 'Too high'

FIX

if guess < secret:
    return 'Too low'

What happens: The player receives a misleading hint.
Compare the guessed number to the secret from the player's perspective.

VERIFY THE STORY

Sources and further reading

Python tutorial: break and continue

Video coming to YouTube

Understand the concept

See it step by step

01. Compare a guess

02. Stop after a match

03. Number attempts

A closer look

Model the game as changing state

Use hints to narrow the search

Keep bad entries from costing a turn

Try it in Python

Python console

Quick quiz

Typical mistakes

Assigning instead of comparing

Reversing the low hint

Sources and further reading