Adding State to PyGame

One of the results from the PyTexas 2019 conference was that I was inspired to add a state machine to my pygame project. When I got back to where I was staying, I had no internet and so I had to create my own state handler class from scratch. I’ve been using Redux for front-end development, and I based my solution a little off that experience.

Here is the code for the simple state handler class I created:

class Machine():
    """
    THIS CLASS IS THE STATE MACHINE FOR THE APPLICATION
    """
    def __init__(self):
        self.transitions = {}
        self.state = APP_PAUSE

    def addTransition(self,**kwargs):
        if kwargs['name'] in self.transitions:
            self.transitions[kwargs['name']]['states'].append(kwargs['state'])
        else:
            self.transitions[kwargs['name']] = {'states':[kwargs['state']]}

    def update(self,state):
        if state in self.transitions and self.state in self.transitions[state]['states']:
            self.state = state
        else:
            print('ERROR: Could Not Switch To State %s From %s' % (state,self.state))

Once I had the Machine class laid out, I started with three states (FORWARD, BACKWARD, and OFF). This described the movement states of the game. This worked extremely well, and significantly reduced the amount of checks I had to perform in the main game loop. As soon as that was done, I began looking for more states to add. I now have several states for this game including:

  • OFF - Which means “in shutdown”.

  • WIN - Which means that the player has won, and the game should display the win screen

  • FAIL - Which means that the player has lost, and the game should display the try again screen.

  • PAUSE - In case the player needs to step away.

  • RESET - Which means the player has won or lost, and is going to play again so reset everything.

  • FORWARD - The player is moving forward.

  • BACKWARD - The player is moving backward..

The state manager not only simplified the code in my main game loop, but it allowed conditionals to be moved into the sprite classes, since the state of the game is global. This makes the sprites “smarter” too.

Next steps will be to implement more fully featured WIN/FAIL/RESET interfaces.

Development, PythonKevin CromwellPyTexas2019