text: import os
  import tracemalloc
  from typing import Dict, Optional, TYPE_CHECKING
  
  from ray.rllib.env import BaseEnv
  from ray.rllib.policy import Policy
  from ray.rllib.policy.sample_batch import SampleBatch
  from ray.rllib.evaluation import MultiAgentEpisode
  from ray.rllib.utils.annotations import PublicAPI
  from ray.rllib.utils.deprecation import deprecation_warning
  from ray.rllib.utils.typing import AgentID, PolicyID
  
  # Import psutil after ray so the packaged version is used.
  import psutil
  
  if TYPE_CHECKING:
      from ray.rllib.evaluation import RolloutWorker
  
  
  @PublicAPI
  class DefaultCallbacks:
      """Abstract base class for RLlib callbacks (similar to Keras callbacks).
  
      These callbacks can be used for custom metrics and custom postprocessing.
  
      By default, all of these callbacks are no-ops. To configure custom training
      callbacks, subclass DefaultCallbacks and then set
      {"callbacks": YourCallbacksClass} in the trainer config.
      """
  
      def __init__(self, legacy_callbacks_dict: Dict[str, callable] = None):
          if legacy_callbacks_dict:
              deprecation_warning(
                  "callbacks dict interface",
                  "a class extending rllib.agents.callbacks.DefaultCallbacks")
          self.legacy_callbacks = legacy_callbacks_dict or {}
  
      def on_episode_start(self,
                           *,
                           worker: "RolloutWorker",
                           base_env: BaseEnv,
                           policies: Dict[PolicyID, Policy],
                           episode: MultiAgentEpisode,
                           env_index: Optional[int] = None,
                           **kwargs) -> None:
          """Callback run on the rollout worker before each episode starts.
  
          Args:
              worker (RolloutWorker): Reference to the current rollout worker.
              base_env (BaseEnv): BaseEnv running the episode. The underlying
                  env object can be gotten by calling base_env.get_unwrapped().
              policies (dict): Mapping of policy id to policy objects. In single
                  agent mode there will only be a single "default" policy.
              episode (MultiAgentEpisode): Episode object which contains episode
                  state. You can use the `episode.user_data` dict to store
                  temporary data, and `episode.custom_metrics` to store custom
                  metrics for the episode.
              env_index (EnvID): Obsoleted: The ID of the environment, which the
                  episode belongs to.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_episode_start"):
              self.legacy_callbacks["on_episode_start"]({
                  "env": base_env,
                  "policy": policies,
                  "episode": episode,
              })
  
      def on_episode_step(self,
                          *,
                          worker: "RolloutWorker",
                          base_env: BaseEnv,
                          episode: MultiAgentEpisode,
                          env_index: Optional[int] = None,
                          **kwargs) -> None:
          """Runs on each episode step.
  
          Args:
              worker (RolloutWorker): Reference to the current rollout worker.
              base_env (BaseEnv): BaseEnv running the episode. The underlying
                  env object can be gotten by calling base_env.get_unwrapped().
              episode (MultiAgentEpisode): Episode object which contains episode
                  state. You can use the `episode.user_data` dict to store
                  temporary data, and `episode.custom_metrics` to store custom
                  metrics for the episode.
              env_index (EnvID): Obsoleted: The ID of the environment, which the
                  episode belongs to.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_episode_step"):
              self.legacy_callbacks["on_episode_step"]({
                  "env": base_env,
                  "episode": episode
              })
  
      def on_episode_end(self,
                         *,
                         worker: "RolloutWorker",
                         base_env: BaseEnv,
                         policies: Dict[PolicyID, Policy],
                         episode: MultiAgentEpisode,
                         env_index: Optional[int] = None,
                         **kwargs) -> None:
          """Runs when an episode is done.
  
          Args:
              worker (RolloutWorker): Reference to the current rollout worker.
              base_env (BaseEnv): BaseEnv running the episode. The underlying
                  env object can be gotten by calling base_env.get_unwrapped().
              policies (dict): Mapping of policy id to policy objects. In single
                  agent mode there will only be a single "default" policy.
              episode (MultiAgentEpisode): Episode object which contains episode
                  state. You can use the `episode.user_data` dict to store
                  temporary data, and `episode.custom_metrics` to store custom
                  metrics for the episode.
              env_index (EnvID): Obsoleted: The ID of the environment, which the
                  episode belongs to.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_episode_end"):
              self.legacy_callbacks["on_episode_end"]({
                  "env": base_env,
                  "policy": policies,
                  "episode": episode,
              })
  
      def on_postprocess_trajectory(
              self, *, worker: "RolloutWorker", episode: MultiAgentEpisode,
              agent_id: AgentID, policy_id: PolicyID,
              policies: Dict[PolicyID, Policy], postprocessed_batch: SampleBatch,
              original_batches: Dict[AgentID, SampleBatch], **kwargs) -> None:
          """Called immediately after a policy's postprocess_fn is called.
  
          You can use this callback to do additional postprocessing for a policy,
          including looking at the trajectory data of other agents in multi-agent
          settings.
  
          Args:
              worker (RolloutWorker): Reference to the current rollout worker.
              episode (MultiAgentEpisode): Episode object.
              agent_id (str): Id of the current agent.
              policy_id (str): Id of the current policy for the agent.
              policies (dict): Mapping of policy id to policy objects. In single
                  agent mode there will only be a single "default" policy.
              postprocessed_batch (SampleBatch): The postprocessed sample batch
                  for this agent. You can mutate this object to apply your own
                  trajectory postprocessing.
              original_batches (dict): Mapping of agents to their unpostprocessed
                  trajectory data. You should not mutate this object.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_postprocess_traj"):
              self.legacy_callbacks["on_postprocess_traj"]({
                  "episode": episode,
                  "agent_id": agent_id,
                  "pre_batch": original_batches[agent_id],
                  "post_batch": postprocessed_batch,
                  "all_pre_batches": original_batches,
              })
  
      def on_sample_end(self, *, worker: "RolloutWorker", samples: SampleBatch,
                        **kwargs) -> None:
          """Called at the end of RolloutWorker.sample().
  
          Args:
              worker (RolloutWorker): Reference to the current rollout worker.
              samples (SampleBatch): Batch to be returned. You can mutate this
                  object to modify the samples generated.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_sample_end"):
              self.legacy_callbacks["on_sample_end"]({
                  "worker": worker,
                  "samples": samples,
              })
  
      def on_learn_on_batch(self, *, policy: Policy, train_batch: SampleBatch,
                            result: dict, **kwargs) -> None:
          """Called at the beginning of Policy.learn_on_batch().
  
          Note: This is called before 0-padding via
          `pad_batch_to_sequences_of_same_size`.
  
          Args:
              policy (Policy): Reference to the current Policy object.
              train_batch (SampleBatch): SampleBatch to be trained on. You can
                  mutate this object to modify the samples generated.
              result (dict): A results dict to add custom metrics to.
              kwargs: Forward compatibility placeholder.
          """
  
          pass
  
      def on_train_result(self, *, trainer, result: dict, **kwargs) -> None:
          """Called at the end of Trainable.train().
  
          Args:
              trainer (Trainer): Current trainer instance.
              result (dict): Dict of results returned from trainer.train() call.
                  You can mutate this object to add additional metrics.
              kwargs: Forward compatibility placeholder.
          """
  
          if self.legacy_callbacks.get("on_train_result"):
              self.legacy_callbacks["on_train_result"]({
                  "trainer": trainer,
                  "result": result,
              })
  
  
  class MemoryTrackingCallbacks(DefaultCallbacks):
      """MemoryTrackingCallbacks can be used to trace and track memory usage
      in rollout workers.
  
      The Memory Tracking Callbacks uses tracemalloc and psutil to track
      python allocations during rollouts,
      in training or evaluation.
  
      The tracking data is logged to the custom_metrics of an episode and
      can therefore be viewed in tensorboard
      (or in WandB etc..)
  
      Add MemoryTrackingCallbacks callback to the tune config
      e.g. { ...'callbacks': MemoryTrackingCallbacks ...}
  
      Note:
          This class is meant for debugging and should not be used
          in production code as tracemalloc incurs
          a significant slowdown in execution speed.
      """
  
      def __init__(self):
          super().__init__()
  
          # Will track the top 10 lines where memory is allocated
          tracemalloc.start(10)
  
      def on_episode_end(self,
                         *,
                         worker: "RolloutWorker",
                         base_env: BaseEnv,
                         policies: Dict[PolicyID, Policy],
                         episode: MultiAgentEpisode,
                         env_index: Optional[int] = None,
                         **kwargs) -> None:
          snapshot = tracemalloc.take_snapshot()
          top_stats = snapshot.statistics("lineno")
  
          for stat in top_stats[:10]:
              count = stat.count
              size = stat.size
  
              trace = str(stat.traceback)
  
              episode.custom_metrics[f"tracemalloc/{trace}/size"] = size
              episode.custom_metrics[f"tracemalloc/{trace}/count"] = count
  
          process = psutil.Process(os.getpid())
          worker_rss = process.memory_info().rss
          worker_data = process.memory_info().data
          worker_vms = process.memory_info().vms
          episode.custom_metrics["tracemalloc/worker/rss"] = worker_rss
          episode.custom_metrics["tracemalloc/worker/data"] = worker_data
          episode.custom_metrics["tracemalloc/worker/vms"] = worker_vms
  
  
  class MultiCallbacks(DefaultCallbacks):
      """MultiCallbacks allows multiple callbacks to be registered at
      the same time in the config of the environment.
  
      Example:
  
          .. code-block:: python
  
              'callbacks': MultiCallbacks([
                  MyCustomStatsCallbacks,
                  MyCustomVideoCallbacks,
                  MyCustomTraceCallbacks,
                  ....
              ])
      """
  
      def __init__(self, callback_class_list):
          super().__init__()
          self._callback_class_list = callback_class_list
  
          self._callback_list = []
  
      def __call__(self, *args, **kwargs):
          self._callback_list = [
              callback_class() for callback_class in self._callback_class_list
          ]
  
          return self
  
      def on_episode_start(self,
                           *,
                           worker: "RolloutWorker",
                           base_env: BaseEnv,
                           policies: Dict[PolicyID, Policy],
                           episode: MultiAgentEpisode,
                           env_index: Optional[int] = None,
                           **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_episode_start(
                  worker=worker,
                  base_env=base_env,
                  policies=policies,
                  episode=episode,
                  env_index=env_index,
                  **kwargs)
  
      def on_episode_step(self,
                          *,
                          worker: "RolloutWorker",
                          base_env: BaseEnv,
                          episode: MultiAgentEpisode,
                          env_index: Optional[int] = None,
                          **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_episode_step(
                  worker=worker,
                  base_env=base_env,
                  episode=episode,
                  env_index=env_index,
                  **kwargs)
  
      def on_episode_end(self,
                         *,
                         worker: "RolloutWorker",
                         base_env: BaseEnv,
                         policies: Dict[PolicyID, Policy],
                         episode: MultiAgentEpisode,
                         env_index: Optional[int] = None,
                         **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_episode_end(
                  worker=worker,
                  base_env=base_env,
                  policies=policies,
                  episode=episode,
                  env_index=env_index,
                  **kwargs)
  
      def on_postprocess_trajectory(
              self, *, worker: "RolloutWorker", episode: MultiAgentEpisode,
              agent_id: AgentID, policy_id: PolicyID,
              policies: Dict[PolicyID, Policy], postprocessed_batch: SampleBatch,
              original_batches: Dict[AgentID, SampleBatch], **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_postprocess_trajectory(
                  worker=worker,
                  episode=episode,
                  agent_id=agent_id,
                  policy_id=policy_id,
                  policies=policies,
                  postprocessed_batch=postprocessed_batch,
                  original_batches=original_batches,
                  **kwargs)
  
      def on_sample_end(self, *, worker: "RolloutWorker", samples: SampleBatch,
                        **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_sample_end(worker=worker, samples=samples, **kwargs)
  
      def on_learn_on_batch(self, *, policy: Policy, train_batch: SampleBatch,
                            result: dict, **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_learn_on_batch(
                  policy=policy,
                  train_batch=train_batch,
                  result=result,
                  **kwargs)
  
      def on_train_result(self, *, trainer, result: dict, **kwargs) -> None:
          for callback in self._callback_list:
              callback.on_train_result(trainer=trainer, result=result, **kwargs)
  