code: def __init__(self, env: Environment, policy: TabularPolicy) -> None:
      self._env = env
      self._policy = policy
  
imports: import pickle
  from functools import reduce
  from typing import List, Mapping, Sequence
  import torch
  from reagent.ope.estimators.sequential_estimators import Model, RLPolicy, State, ValueFunction
  from reagent.ope.estimators.types import Action, ActionDistribution, ActionSpace
  from reagent.ope.test.envs import Environment, PolicyLogGenerator
  from reagent.ope.utils import RunningAverage
label_desc: Use image node_id 1 to create a new DPTrainer object  with example: obj = DPTrainer(env, policy)