Gym-MiniGrid/gym_minigrid/envs/keycorridor.py

from gym_minigrid.roomgrid import RoomGrid


class KeyCorridorEnv(RoomGrid):
    """
    A ball is behind a locked door, the key is placed in a
    random room.
    """

    def __init__(self, num_rows=3, obj_type="ball", room_size=6, **kwargs):
        self.obj_type = obj_type

        super().__init__(
            room_size=room_size,
            num_rows=num_rows,
            max_steps=30 * room_size**2,
            **kwargs,
        )

    def _gen_grid(self, width, height):
        super()._gen_grid(width, height)

        # Connect the middle column rooms into a hallway
        for j in range(1, self.num_rows):
            self.remove_wall(1, j, 3)

        # Add a locked door on the bottom right
        # Add an object behind the locked door
        room_idx = self._rand_int(0, self.num_rows)
        door, _ = self.add_door(2, room_idx, 2, locked=True)
        obj, _ = self.add_object(2, room_idx, kind=self.obj_type)

        # Add a key in a random room on the left side
        self.add_object(0, self._rand_int(0, self.num_rows), "key", door.color)

        # Place the agent in the middle
        self.place_agent(1, self.num_rows // 2)

        # Make sure all rooms are accessible
        self.connect_all()

        self.obj = obj
        self.mission = f"pick up the {obj.color} {obj.type}"

    def step(self, action):
        obs, reward, done, info = super().step(action)

        if action == self.actions.pickup:
            if self.carrying and self.carrying == self.obj:
                reward = self._reward()
                done = True

        return obs, reward, done, info