Microbit Infection

Infection is a multi-player game that can be played using the radio to model the spread of an infection through a population. I couldn’t find an implementation in Python so thought we should create one for our codind dojo. Here is one approach using an OO model to handle the progression of a disease in a host from healthy to sick and (the great) beyond.

Player

We can start with a player class to model how we think about progression of the infection. At some point we will come in contact with an infected person and need to decide if we pick up the infection from them. Once infected we will pass on the infection and we need a way to signal that the game is over with. Our game loop and initial player looks like this.


from microbit import *
import radio

radio.config(power=0) # low power ~ 1 meter distance
radio.on()

class Player:

    def transmit_infection(self):
        pass
        
    def contract_infection(self):
        return self
        
    def incubate(self):
        return self
        
    def done(self):
        return False


player = Player()

while not player.done():
    
    player.transmit_infection()
    player = player.contract_infection()
    player = player.incubate()

    display.show(player.face)
    sleep(100)


Contract and Incubate methods are opportunities for a state change so in the normal case we just return “ourselves” but we have the option to override this behaviour in subclasses to return a different patient “state”. We will derive new states from the Player to model the stages of the spread of the disease.

Healthy

According to the rules, a healthy player is happy but can contract an illness. So we need a way to specify what an illness looks like and the rules around transmitting it and contracting it.

Illness



class Illness:

    def __init__(self):
        self.dna = 'virus'
            
    def transmit(self):
        radio.send(self.dna)
        
    def is_contagious(self):
        
        packet = radio.receive_full()

        if packet:
            text = message[0]
            signal_strength = message[1]

            # random chance?
            # signal strength ?
            return text == self.dna
       
        return False


Sending the virus is easy, we broadcast the word virus to all those around us. Checking whether an virus is contagious gives us some space to get creative. We can just identify the word as the easiest thing or use a combination of random chance, look at the signal strength of the recevied message to see if the person is “close enough” or something else. The important thing is the decision logic is encapsulated within the Illness itself.

The Great Beyond

Let’s jump straight to the end and look at what death looks like.


class Dead(Player):
    
    def __init__(self):
        self.face = Image.GHOST
        
    def done(self):
        return True


For this case we are saying a dead patient is shown by the ghost and the “done” flag tells us the game is over.

Healthy Again

Turning our attention to the healthy player, we can instantiate one in the place of our first player so that we start off the game in a good state. Healthy players are happy but also have a chance of catching an infection so we need to check for this by asking if an received illness is contagious.


class Healthy(Player):
    
    def __init__(self):
        self.face = Image.HAPPY

    def contract_infection(self):
        illness = Illness()
        return Infected() if illness.is_contagious() else self

    def incubate(self):
        if button_a.was_pressed() and button_b.was_pressed():
            return Infected()

        return self


We also override the incubate method to give us a quick way of simulating a patient zero condition. Pressing both buttons will turn a healthy person into a suitably infected person.

Infected

An infected person is able to transmit an illness to those around them according to illness rules. They can also incubate for a set period of time before transitioning into a Sick person so we setup a timer and increment it every time we do an incubate in the loop.


class Infected(Player):

    def __init__(self):
        self.face = Image.CONFUSED
        self.timer = 0
        
    def transmit_infection(self):
        illness = Illness()
        illness.transmit()
        
    def incubate(self):
        self.timer += 1
        return Sick() if self.timer > 1000 else self


Note I am using the confused icon to represent this state for debugging but in a real game this would be replaced with the happy icon so no one is able to tell that you are a contagious person, in line with the original rules.

Sick

Similar to the Infected role, a sick person has a timer associated with it so that they only stay sick for a certain period. They have a different icon so we can tell they are sick but they are no longer infectious so don’t spread the disease any further.


class Sick(Player):
        
    def __init__(self):
        self.face = Image.SKULL
        self.timer = 0

    def incubate(self):
        self.timer += 1
        return Dead() if self.timer > 1000 else self
        

And that’s it for all the stages of the game. We need an initiator to kick off the first sick person but that can be done without the healthy person test code and could be done with some bespoke code run on a separate device. It might also be interesting to see how things play out if a person could recover from an infection, if a sick person also was able to continue spreading infection or if the later stages of the infection proceeded quicker than in this example.