code: def _sample_candidates(self):
      self.candidates = [
          random_document(self._doc_sampler)
          for _ in range(self.slate_size)
      ]
      n = len(self.candidates)
      return {
          "user": np.zeros((1,)),
          "doc": {
              str(k): np.array(self.candidates[k], dtype=np.float32)
              for k in range(n)
          },
      }
  
imports: from collections import namedtuple
  from typing import List, Optional
  import gym
  import numpy
  from gym.utils import seeding
  from gym.wrappers.time_limit import TimeLimit
  from reagent.core.dataclasses import dataclass
  from reagent.gym.envs.env_wrapper import EnvWrapper
  from reagent.gym.envs.recsim import RecsimObsPreprocessor
  from reagent.gym.envs.wrappers.recsim import ValueWrapper
  from scipy.special import expit, logit
label_desc: Use image node_id 3 for calling the ToyVMEnv obj's underlying member method code with example usage: obj._sample_candidates() and returns: dict