问Creating a textadventure in python: AttributeError: module x has no attribute y

EN

import game
class MapTile:
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def intro_text(self):
        raise NotImplementedError("Create a subclass instead!")


class StartTile(MapTile):
    def intro_text(self):
        return "some text, " + user_name + """ even more text
    """

class BoringTile(MapTile):
    def intro_text(self):
        return """
        some text
        """

class VictoryTile(MapTile):
    def intro_text(self):
        return """
        some text
        """

world_map = [
[None, VictoryTile(1,0), None],
[None, BoringTile(1,1), None],
[BoringTile(0,2),StartTile(1,2),BoringTile(2,2)],
[None,BoringTile(1,3),None]
]

def tile_at(x, y):
    if x < 0 or y < 0:
        return None
    try:
        return world_map[y][x]
    except IndexError:
         return None

import world
from player import Player


def play():

print("------------------------------------")
print("         Willkommen zu ...")
print("------------------------------------" + "\n")
player = Player()

while True:
    user_name = get_user_name()
    room = world.tile_at(player.x, player.y)
    print(room.intro_text())
    action_input = get_player_command()
    if action_input in ["n", "N"]:
        player.move_north()
    elif action_input in ["s", "S"]:
        player.move_south()
    elif action_input in ["o", "O"]:
        player.move_east()
    elif action_input in ["w", "W"]:
        player.move_west()
    elif action_input in ["i", "I"]:
        player.print_inventory()

def get_user_name():
    return input("text " + "\n")    

def get_player_command():
    return input()

def print_ordered(to_print):
    for i, value in enumerate(to_print, 1):
        print(str(i) + ". " + str(value))

play()

Traceback (most recent call last):
  File "C:\Users\samwa\Workspace\TextAdventure\game.py", line 1, in <module>
    import world
  File "C:\Users\samwa\Workspace\TextAdventure\world.py", line 1, in <module>
    import game
  File "C:\Users\samwa\Workspace\TextAdventure\game.py", line 38, in <module>
    play()
  File "C:\Users\samwa\Workspace\TextAdventure\game.py", line 14, in play
    room = world.tile_at(player.x, player.y)
AttributeError: module 'world' has no attribute 'tile_at'