disk_player.py

from enum import Enum, auto


class State(Enum):
    EMPTY = auto()
    STOPPED = auto()
    PAUSED = auto()
    PLAYING = auto()


class DiskPlayer:
    def __init__(self):
        self.state = State.EMPTY

    def insert_disk(self):
        if self.state is State.EMPTY:
            self.state = State.STOPPED
        else:
            raise ValueError("disk already inserted")

    def eject_disk(self):
        if self.state is State.EMPTY:
            raise ValueError("no disk inserted")
        else:
            self.state = State.EMPTY

    def play(self):
        if self.state in {State.STOPPED, State.PAUSED}:
            self.state = State.PLAYING

    def pause(self):
        if self.state is State.PLAYING:
            self.state = State.PAUSED
        else:
            raise ValueError("can't pause when not playing")

    def stop(self):
        if self.state in {State.PLAYING, State.PAUSED}:
            self.state = State.STOPPED
        else:
            raise ValueError("can't stop when not playing or paused")


if __name__ == "__main__":
    actions = [
        DiskPlayer.insert_disk,
        DiskPlayer.play,
        DiskPlayer.pause,
        DiskPlayer.stop,
        DiskPlayer.eject_disk,
        DiskPlayer.insert_disk,
        DiskPlayer.play,
        DiskPlayer.stop,
        DiskPlayer.eject_disk,
    ]
    player = DiskPlayer()
    for action in actions:
        action(player)
        print(player.state)