03_guess_the_number.md

Chapter 3: Guess the Number

Based on: http://inventwithpython.com/invent4thed/chapter3.html

In this chapter, you’re going to make a Guess the Number game. The computer will think of a secret number from 1 to 20 and ask the user to guess it. After each guess, the computer will tell the user whether the number is too high or too low. The user wins if they can guess the number within six tries.

This is a good game to code because it covers many programming concepts in a short program. You’ll learn how to convert values to different data types and when you would need to do this. Since this program is a game, from now on we’ll call the user the player.

Part 1. Create a New Script

Follow the instructions in Repl.it Tips to create a new file called "guess.py" and change your .replit file to run it.

Add a comment to the first line of the script to describe it:

Edit Your Script

guess.py

"""This is a Guess the Number game."""

Part 2. Use the random Module

Python has a limited set of functions built into the language like the print() function that you are already familiar with. More functions can be accessed through modules.

A module is a kind of reusable code that can be loaded into your scripts using the import keyword.

We are going to use the random module in this script. It has a function randint() which we will use to get a random number.

To call a function that is part of a module, put the module namespace in front of the function followed by a dot, then the function name.

The randint() function takes two arguments. The first is the minimum number, the second is the maximum number.

Try it in the Python Shell

In the right pane of your repl.it, if you see only one > open a python shell by typing python3 then hitting enter. The prompt will change to >>>.

> python3
Python 3.8.3 (default, May 14 2020, 20:11:43)
[GCC 7.5.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>>

Now in the Python shell:

>>> import random
>>> random.randint(1,20)

Hint: In the Python shell, you can hit the up arrow to fill in the last line you typed again.

Edit Your Script

Now that you understand how importing works, import the module, then save a random number to the number variable by calling random.randint().

Let's also set the maximum number of guesses.

guess.py

"""This is a Guess the Number game."""
import random

number = random.randint(1, 20)
max_guesses = 6

Part 3: Welcome the Player

We've used the input() function before to get feedback from the user. It can take an optional argument, a string that will be presented to the user as a prompt just to the left of their cursor.

Let's use this new way of calling input() to get the players name and then use print() to greet them.

Edit Your Script

guess.py

"""This is a Guess the Number game."""
import random

number = random.randint(1, 20)
max_guesses = 6

player = input("Hello! What is your name? ")
print("Hello " + player + ".")
print("I am thinking of a number between 1 and 20.")
print()

Note the space after the ? in the input() line. This way there will be a space between the prompt and the cursor.

Part 4: Let the Player Guess

We've used a for loop before to loop over items in a list. Here we will use the range() function, which allows us to easily repeat the loop a specific number of times. We will give it two arguments: the starting number and the max_guesses that we defined earlier.

We've also the print() function before but in the past we've always passed it only one argument. It can take as many arguments as you want and it will convert them each to strings and then print them with spaces in-between. Let's use this handy way to print the guess number each round.

Edit Your Script

guess.py

"""This is a Guess the Number game."""
import random

number = random.randint(1, 20)
max_guesses = 6

player = input("Hello! What is your name? ")
print("Hello " + player + ".")
print("I am thinking of a number between 1 and 20.")

for guess_count in range(1, max_guesses):
    print("Guess", guess_count, "of", max_guesses)
    guess = input("Your guess: ")

Part 5: Check the Guess

The value in the guess variable is a string, because input() always returns a string. But we need a number variable to check the guess. To convert a string to an integer, we will use the int() function.

Once it is converted, we can use an if statement to check it. We'll use the break keyword to exit the loop early if the guess is correct.

"""This is a Guess the Number game."""
import random

number = random.randint(1, 20)
max_guesses = 6

player = input("Hello! What is your name? ")
print("Hello " + player + ".")
print("I am thinking of a number between 1 and 20.")
print()

for guess_count in range(1, max_guesses):
    print("Guess", guess_count, "of", max_guesses)

    guess = input("Your guess: ")
    guess = int(guess)

    if guess < number:
        print('Your guess is too low.')

    elif guess > number:
        print('Your guess is too high.')

    else:
        break

    print()

Part 6: Check if the Player Won

When the code runs to the point where it exits the for loop both the guess and the guess_count variables will still be the last value each was set to when the loop ran for the final time.

We'll use an if statement to check the guess value to determine if the player won or not and print out a message for each case.

Both the guess variable and the number variable are integers but we need them to be strings in order to concatonate them in the message we print at the of the game. To convert an int to a string use the str() function.

Edit Your Script

guess.py

"""This is a Guess the Number game."""
import random

number = random.randint(1, 20)
max_guesses = 6

player = input("Hello! What is your name? ")
print("Hello " + player + ".")
print("I am thinking of a number between 1 and 20.")
print()

for guess_count in range(1, max_guesses):
    print("Guess", guess_count, "of", max_guesses)

    guess = input("Your guess: ")
    guess = int(guess)

    if guess < number:
        print('Your guess is too low.')

    elif guess > number:
        print('Your guess is too high.')

    else:
        break

    print()


if guess == number:
    guess_count = str(guess_count)
    print("Good job, " + player + "! You guessed my number in " + guess_count + " guesses!")

else:
    number = str(number)
    print("Nope. The number I was thinking of was " + number + ".")

Part 7: Make it your own

Change the game to make it your own. Here are some ideas.

• Check to see if the player name is your own. If it is, let yourself cheat by printing out the number.

• Make two lists of strings called winner_messages and loser_messages. Randomly choose an item from the appropriate list and print it at the end of the game. Hint: You can use the len() function to find the length of a list.

• Ask the user if they want to play on easy, normal or hard mode when they start, then change the number of guesses or the range of possible numbers based on their answer.

• Keep track of how far away each guess is from the right number. If they get further away, print out an extra message to let them know.

• Don't end after the player wins or loses, but instead offer them the chance to play again. Keep track of their wins, losses and total number of games played and print it at the end of each round.

What we've learned

• How to import a module and call its functions.
• How to convert between strings and integers.
• How to use the range() function in a for loop.
• How to pass a prompt argument to the input() function.
• How to pass multiple arguments to the print() function to easily print spaces between them.