Project: Number guessing game

Milestone 1: one guess

Start with a secret number you choose yourself, and a single guess. Don't forget lesson 1.5: input() gives you text.

secret = 42
# Ask for a guess, then print Too high, Too low, or You got it!

secret = 42
guess = int(input("Guess: "))
if guess > secret:
    print("Too high")
elif guess < secret:
    print("Too low")
else:
    print("You got it!")

Milestone 2: keep guessing

Now repeat until the guess is right, and count the attempts. That's two plans you know: guess is a latest value, and attempts is a counter. Where the counter goes up matters. Predict what this version says at the end:

secret = 42
attempts = 0
while True:
    guess = int(input("Guess: "))
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        attempts = attempts + 1
        print(f"You got it in {attempts} attempts!")
        break

Guess: 50
Too high
Guess: 25
Too low
Guess: 42
You got it in 1 attempts!

secret = 42
guess = int(input("Guess: "))
if guess > secret:
    print("Too high")
elif guess < secret:
    print("Too low")
else:
    print("You got it!")

secret = 42
attempts = 0
while True:
    guess = int(input("Guess: "))
    attempts = attempts + 1
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        print(f"You got it in {attempts} attempts!")
        break

Milestone 3: a random secret

A game where you know the answer isn't much of a game. Python's random module picks numbers for you. import random makes it available (lesson 8.5 explains imports), and random.randint(1, 100) picks a whole number from 1 to 100.

randint includes both ends: it can pick 1, and it can pick 100. That's different from range(1, 100), which stops before 100. Mixing the two up is a classic bug.

A random secret makes the output different every time, which makes it hard to check. random.seed(2019) fixes that: after it, the "random" numbers come out the same on every run, so this lesson can show you exactly what to expect. With this seed, the secret is 20. When your game works, delete the seed line and play for real.

secret = 42
attempts = 0
while True:
    guess = int(input("Guess: "))
    attempts = attempts + 1
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        print(f"You got it in {attempts} attempts!")
        break

import random

random.seed(2019)
secret = random.randint(1, 100)
attempts = 0
while True:
    guess = int(input("Guess: "))
    attempts = attempts + 1
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        print(f"You got it in {attempts} attempts!")
        break

Milestone 4: bad guesses don't count

Players mistype. A guess that isn't a number shouldn't crash the game, and a guess outside 1 to 100 shouldn't cost an attempt. Read the guess as text first. Then text.isdigit() tells you whether the text is all digits (True or False); you'll meet more tools like it in Module 6. Skip bad guesses with continue, before the counter goes up.

import random

random.seed(2019)
secret = random.randint(1, 100)
attempts = 0
while True:
    guess = int(input("Guess: "))
    attempts = attempts + 1
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        print(f"You got it in {attempts} attempts!")
        break

import random

random.seed(2019)
secret = random.randint(1, 100)
attempts = 0
while True:
    text = input("Guess: ")
    if not text.isdigit():
        print("Please type a whole number.")
        continue
    guess = int(text)
    if guess < 1 or guess > 100:
        print("Guess from 1 to 100.")
        continue
    attempts = attempts + 1
    if guess > secret:
        print("Too high")
    elif guess < secret:
        print("Too low")
    else:
        print(f"You got it in {attempts} attempts!")
        break

That's the complete game. Test it with the three kinds of game a player can have: one you win, one full of typos, and, after the stretch, one you lose. (isdigit() isn't a perfect test: it turns away -5, which int() accepts, and lets through a few characters int() can't convert, like ፩. Lesson 7.2 shows the better way: try int() and handle the error.)

Milestone 5: seven tries, and play again (stretch)

With halving (guess the middle, then the middle of what's left), you never need more than 7 guesses for 1 to 100: each guess cuts the possibilities in half, and 100 halves to 1 in seven steps. So a limit of 7 attempts is fair. That idea, halving, is one of the most important in computing, and it comes back later in the course.

Add the limit with a constant, MAX_ATTEMPTS = 7, and a flag, won: it starts False and becomes True when the player wins, so after the loop you know which way it ended. Then wrap the whole game in an outer loop that asks to play again.

import random

random.seed(2019)
MAX_ATTEMPTS = 7
# One game per round of an outer loop; inside it, your game from milestone 4,
# stopping after MAX_ATTEMPTS attempts

import random

random.seed(2019)
MAX_ATTEMPTS = 7
while True:
    secret = random.randint(1, 100)
    attempts = 0
    won = False
    while attempts < MAX_ATTEMPTS:
        text = input("Guess: ")
        if not text.isdigit():
            print("Please type a whole number.")
            continue
        guess = int(text)
        if guess < 1 or guess > 100:
            print("Guess from 1 to 100.")
            continue
        attempts = attempts + 1
        if guess > secret:
            print("Too high")
        elif guess < secret:
            print("Too low")
        else:
            print(f"You got it in {attempts} attempts!")
            won = True
            break
    if not won:
        print(f"Out of attempts! The number was {secret}.")
    again = input("Play again? (y/n) ")
    if again != "y":
        break

Change the last n in the Input box to y, then add guesses for a second game. The seed makes the second secret 32: can you find it in 7?