class_docstr: Generates trackers from training data.
class_docstr_tok: ["Generates","trackers","from","training","data","."]
docstr: Filter active trackers that ended with unused checkpoint
  or are parts of loops.
docstr_tok: ["Filter","active","trackers","that","ended","with","unused","checkpoint","or","are","parts","of","loops","."]
code: def _filter_active_trackers(
      active_trackers: TrackerLookupDict, unused_checkpoints: Set[Text]
  ) -> TrackerLookupDict:
      """Filter active trackers that ended with unused checkpoint
      or are parts of loops.
      """
      next_active_trackers = defaultdict(list)
  
      for start_name in unused_checkpoints:
          # process trackers ended with unused checkpoints further
          if start_name != STORY_START:
              # there is no point to process STORY_START checkpoint again
              next_active_trackers[start_name] = active_trackers.get(
                  start_name, []
              )
  
      return next_active_trackers
  
imports: from collections import defaultdict, namedtuple, deque
  import copy
  import logging
  import random
  from contextlib import contextmanager
  from tqdm import tqdm
  from typing import Optional, List, Text, Set, Dict, Tuple, Deque, DefaultDict, Any, Iterable, Generator
  from rasa.shared.constants import DOCS_URL_STORIES
  from rasa.shared.core.constants import SHOULD_NOT_BE_SET
  from rasa.shared.core.domain import Domain, State
  from rasa.shared.core.events import ActionExecuted, UserUttered, ActionReverted, UserUtteranceReverted, Restarted, Event, SlotSet, ActiveLoop
  from rasa.shared.core.trackers import DialogueStateTracker, FrozenState
  from rasa.shared.core.slots import Slot
  from rasa.shared.core.training_data.structures import StoryGraph, STORY_START, StoryStep, RuleStep, GENERATED_CHECKPOINT_PREFIX
  from rasa.shared.utils.io import is_logging_disabled
  import rasa.shared.utils.io
label_desc: Use image node_id 11 for calling the TrainingDataGenerator obj's underlying member method code with example usage: obj._filter_active_trackers(active_trackers, unused_checkpoints) and returns: next_active_trackers