class_docstr: An input filter is a module that filters the input from an environment to the agent.
class_docstr_tok: ["An","input","filter","is","a","module","that","filters","the","input","from","an","environment","to","the","agent","."]
docstr: Save the filter's internal state to a checkpoint to file, so that it can be later restored.
  :param checkpoint_dir: the directory in which to save the filter's state
  :param checkpoint_prefix: the prefix of the checkpoint file to save
  :return: None
code: def save_state_to_checkpoint(self, checkpoint_dir, checkpoint_prefix):
      """
      Save the filter's internal state to a checkpoint to file, so that it can be later restored.
      :param checkpoint_dir: the directory in which to save the filter's state
      :param checkpoint_prefix: the prefix of the checkpoint file to save
      :return: None
      """
      checkpoint_prefix = ".".join([checkpoint_prefix, "filters"])
      if self.name is not None:
          checkpoint_prefix = ".".join([checkpoint_prefix, self.name])
      for filter_name, filter in self._reward_filters.items():
          curr_reward_filter_ckpt_prefix = ".".join(
              [checkpoint_prefix, "reward_filters", filter_name]
          )
          filter.save_state_to_checkpoint(
              checkpoint_dir, curr_reward_filter_ckpt_prefix
          )
  
      for (
          observation_name,
          filters_dict,
      ) in self._observation_filters.items():
          for filter_name, filter in filters_dict.items():
              curr_obs_filter_ckpt_prefix = ".".join(
                  [
                      checkpoint_prefix,
                      "observation_filters",
                      observation_name,
                      filter_name,
                  ]
              )
              filter.save_state_to_checkpoint(
                  checkpoint_dir, curr_obs_filter_ckpt_prefix
              )
  
imports: import copy
  import os
  from collections import OrderedDict
  from copy import deepcopy
  from typing import Dict, Union, List
  from rl_coach.core_types import EnvResponse, ActionInfo, Transition
  from rl_coach.spaces import ActionSpace, RewardSpace, ObservationSpace
  from rl_coach.utils import force_list
label_desc: Use image node_id 18 for calling the InputFilter obj's underlying member method code with example usage: obj.save_state_to_checkpoint(checkpoint_dir, checkpoint_prefix) without return types