class_docstr: A dummy flat policy 
class_docstr_tok: ["A","dummy","flat","policy"]
docstr: compute top action 
docstr_tok: ["compute","top","action"]
code: def compute_top_action_candidates(
      self, observation: ObservationType, num_candidates: Optional[int]
  ) -> Tuple[Sequence[ActionType], Sequence[float]]:
      """compute top action"""
      raise NotImplementedError
  
file_path: maze/maze/test/core/agent/test_default_policy.py
imports: from typing import Tuple, Sequence, Optional
  import numpy
  from maze.core.agent.default_policy import DefaultPolicy
  from maze.core.agent.flat_policy import FlatPolicy
  from maze.core.env.action_conversion import ActionType
  from maze.core.env.observation_conversion import ObservationType
  from maze.core.env.structured_env import ActorID
label_desc: Use image node_id 3 for calling the DummyFlatPolicy obj's underlying member method code with example usage: obj.compute_top_action_candidates(observation, num_candidates) without return types