Question

I’m creating a small game using Python with the module Pygame.

I tried implementing a pretty basic (and I guess a pretty naive) state manager.

However,
I currently have an issue :
once I switch the the “play” state, I can’t switch back to the “menu”.
Is this a flaw in how I designed my state manager?

I have two methods,

1. The state_change method takes one argument, the desired state.
2. The state_check method takes a state as the only argument and returns it as the current state.

Here are the two methods:

def state_check(self, state):
    self.current_state = state
    print self.current_state
    return self.current_state

def state_change(self, state):
    self.state = state

Before the main loop,
The first state is initialized to be “menu”.
Inside the main loop,
state_check is before the if-statements to indicate which state the start with.

def game_loop(self):                                                                       

    running = True
    self.test_car = car()
    self.state = "menu"
    while running:
        pygame.display.set_caption("Project G")
        self.state_check(self.state)
        if self.current_state ==  "menu":
            self.state_check(self.state)
            self.screen.blit(self.background, (0,0))
            #Blits the current state on the screen for testing purposes.
            self.screen.blit(self.menu_text, (700, 580))
            self.event_handler()
            pygame.display.flip()
        if self.current_state == "play":
            self.state_check(self.state)
            self.screen.blit(self.background, (0,0))
            #Blits the current state on the screen.
            self.screen.blit(self.play_text, (700, 580))
            self.test_car.event_handler()
            self.test_car.update(self.test_car.x_speed, self.test_car.y_speed)
            pygame.display.flip()

Within the if-statements,
Are the event handler methods, which I’ve currently made to take keyboard inputs to switch between states (By calling the state_change method) and to quit the program.

Using some print methods, I’ve ruled out the possibility of the keys not registering.

#Event handler for the menu

def event_handler(self):

    for event in pygame.event.get():
        if event.type == QUIT:
           pygame.quit()
           sys.exit()
        if event.type == KEYDOWN:
            if event.key == K_p:
                self.state_change("play")
                print "Key Pressed: p"
            if event.key == K_q:
                print "Key Pressed: q"
                pygame.quit()
                sys.exit()

#Sample of the Event handler for "play"

def event_handler(self):
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()
        if event.type == KEYDOWN:
            if event.key == K_m:
                self.state_change("menu")
                print "Key Pressed: m"
            if event.key == K_q:
                print "Key Pressed: q"
                pygame.quit()
                sys.exit()

Answer 1

I think you’re over-complicating things a little – do you really need check_state and set_state functions, and two variables?

I would do something like this:

class State(object):
    menu = "menu"
    play = "play"

class Game(??):

    def event_handler(self):
        for event in pygame.event.get():
            if event.type == KEYDOWN:
                if event.key == K_m:
                    self.state = State.menu
                    print "Key Pressed: m"
                elif event.key == K_p:
                    self.state = State.play
                    print "Key Pressed: p"

    def game_loop(self):
        self.state = State.menu

        while running:
            if self.state is State.menu:
                # Do menu things
            elif self.state is State.play:
                # Play game!