5. Reaction Game with Micro:bit

Quick Overview of Day

Play Micro:bit reaction game, and discuss how the code works. Add features to the game, if time.

5.1. Micro:bit Reaction Game

In this game, you and a friend will compete to see who has faster reactions. After clicking Run, your Micro:bit will wait between 1 and 5 seconds, then display a happy face image. Whichever player presses their button (A or B) first gets one point. Be careful! If you click your button too soon, you will lose 2 points!

# Mico:bit Reaction Game
# Computer Science 20
# Dan Schellenberg

import microbit
import random
import time

def button_clicked(current_score, should_be_pressing):
    """Adds or subtracts from the current score, based on whether an image is showing."""
    if should_be_pressing == True:
        current_score = current_score + 1
        current_score = current_score - 2

    return current_score

def show_winner(a_score, b_score):
    """Print winner to console, and display winner on Micro:bit."""
    if a_score > b_score:
        print("Player A wins!")
        print("Player B wins!")

# global variables
a_score = 0
b_score = 0
someone_pressed_button = True
showing_image = False
time_to_wait = 0
starting_time = 0
ending_time = 0

# constants

# game loop
while True:
    # check if need to pick a new amount of time to wait
    if someone_pressed_button == True:
        showing_image = False

        # pausing execution for 0.5 seconds stops players from accidentally clicking more than once

        # determine when the image should reappear on the microbit
        time_to_wait = random.randrange(1, 6)
        starting_time = time.time()  # unit is seconds

        someone_pressed_button = False

    # check if it is time to display the image
    time_now = time.time()
    time_since_start = time_now - starting_time

    # uncomment the following line to understand how the time works
    # print(time_since_start)

    # change the boolean to turn on the image if enough time has gone by
    if time_since_start > time_to_wait:
        showing_image = True

    # display image if enough time has elapsed
    if showing_image == True:

    # deal with a button being pressed
    if microbit.button_a.is_pressed():
        a_score = button_clicked(a_score, showing_image)
        print("Player A:", a_score, "    Player B:", b_score)
        someone_pressed_button = True

    if microbit.button_b.is_pressed():
        b_score = button_clicked(b_score, showing_image)
        print("Player A:", a_score, "    Player B:", b_score)
        someone_pressed_button = True

    # if somebody wins, end the game
    if a_score >= POINTS_TO_WIN_GAME or b_score >= POINTS_TO_WIN_GAME:

show_winner(a_score, b_score)
print("Game over!")

5.2. New Ideas Used in the Reaction Game

As you read through the reaction game code, there are a number of things that may deserve some explanation. Notice that the structure of the code is generally:

  • comment header
  • import statements
  • function definitions
  • global variables / constants
  • main code

Although you do not have to follow the structure given above exactly, it does provide a reasonable way to organize your code.

Another thing you likely noticed is that I used ALL_CAPS when creating a constant. In Python, a constant is just a regular variable (so it behaves the exact same way as any other variable). However, a common convention is to use ALL_CAPITAL_LETTERS_IN_THE_VARIABLE_NAME, which simply reminds us as programmers that this is a variable whose value should never be changed within our code.

I also used a new function from the time module in this program. time.time() returns the number of seconds that have elapsed since the epoch, which is how your computer keeps track of what the current time is. To understand what this means, call time.time() in Thonny’s shell a few times. Notice that the number you get back from the function is a really large number, and that it has increased each time you call the function. It is important to realize that the unit of this number is seconds. You might find it helpful to uncomment the line containing print(time_since_start) to help you understand the time.time() function.


The Python docs section on time define the epoch as “the point where the time starts, and is platform dependent. For Unix, the epoch is January 1, 1970, 00:00:00 (UTC). To find out what the epoch is on a given platform, look at time.gmtime(0).”

The break command forces the nearest enclosing loop to terminate. In this case, it allows us to exit the while True infinite loop when one of the players has earned enough points to win the game.

5.3. Adapt the Code

Try the following with a partner (the person you were playing the game with):

  • change the game so that you need only 3 points to win the game
  • change the game so that a click at the wrong time makes you only lose 1 point instead of 2

5.3.1. Extra for Experts

  • change the game so that either a HAPPY face or a SKULL can be displayed. If it is a HAPPY face and a user clicks, they should get a point. However, if it is a SKULL and the user clicks, they should lose a point.
Next Section - 1. Nested Loops and Image Processing