How to change an image of a Sprite during the animation?

Question

I want to change an image of the object worker each time when it stops.

The class Worker is created based on the answer of @sloth in this threa

Answer 1

I think you should introduce some kind of state to indicate that the worker is running or not. Here's an example. Note the comments:

class Worker(pygame.sprite.Sprite):

    # we introduce to possible states: RUNNING and IDLE
    RUNNING = 0
    IDLE = 1

    def __init__(self, location, *groups):

        # each state has it's own image
        self.images = {
            Worker.RUNNING: pygame.transform.scale(get_image("worker.png"), (40, 40)),
            Worker.IDLE: pygame.transform.scale(get_image("worker_stopped.png"), (40, 40))
        }

        self._layer = 1
        pygame.sprite.Sprite.__init__(self, groups)

        # let's keep track of the state and how long we are in this state already            
        self.state = Worker.IDLE
        self.ticks_in_state = 0

        self.image = self.images[self.state]
        self.rect = self.image.get_rect(topleft=location)

        self.direction = pygame.math.Vector2(0, 0)
        self.speed = random.randint(2, 4)
        self.set_random_direction()

    def set_random_direction(self):
        # random new direction or standing still
        vec = pygame.math.Vector2(random.randint(-100,100), random.randint(-100,100)) if random.randint(0, 5) > 1 else pygame.math.Vector2(0, 0)

        # check the new vector and decide if we are running or fooling around
        length = vec.length()
        speed = sum(abs(int(v)) for v in vec.normalize() * self.speed) if length > 0 else 0

        if length == 0 or speed == 0:
            new_state = Worker.IDLE
            self.direction = pygame.math.Vector2(0, 0)
        else:
            new_state = Worker.RUNNING
            self.direction = vec.normalize()

        self.ticks_in_state = 0
        self.state = new_state

        # use the right image for the current state
        self.image = self.images[self.state]

    def update(self, screen):
        self.ticks_in_state += 1
        # the longer we are in a certain state, the more likely is we change direction
        if random.randint(0, self.ticks_in_state) > 30:
            self.set_random_direction()

        # now let's multiply our direction with our speed and move the rect
        vec = [int(v) for v in self.direction * self.speed]
        self.rect.move_ip(*vec)

        # if we're going outside the screen, change direction
        if not screen.get_rect().contains(self.rect):
            self.direction = self.direction * -1

        self.rect.clamp_ip(screen.get_rect())