code: def move_down_policy(board, ship):
      act = nearby_enemy(board, ship)
      if act is not None:
          ship.next_action = act
      else:
          ship.next_action = ShipAction.DOWN
  
imports: import base64
  import pickle
  import random
  import numpy
  from zerosum_env.envs.halite.helpers import *
  from zerosum_env import make, evaluate
  from collections import deque
  import parl
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddle.distribution import Categorical
label_desc: Use image node_id 19 for calling a global function with example usage: move_down_policy(board, ship) without return types