# Tracker

Trackers maintain the state of a dialogue between the assistant and the user in the form of conversation sessions. To learn more about how to configure the session behavior, check out the docs on [Session configuration](https://legacy-docs-v1.rasa.com/1.10.20/core/domains/#session-config).

## `class rasa.core.trackers.DialogueStateTracker(sender_id, slots, max_event_history=None, sender_source=None)`

Maintains the state of a conversation.

The field max_event_history will only give you these last events, it can be set in the tracker_store.

### Methods

- **`applied_events()`**  
  Returns all actions that should be applied - w/o reverted events.  
  Return type: `List[Event]`

- **`as_dialogue()`**  
  Return a `Dialogue` object containing all of the turns.  
  This can be serialised and later used to recover the state of this tracker exactly.  
  Return type: `Dialogue`

- **`change_form_to(form_name)`**  
  Activate or deactivate a form  
  Return type: `None`

- **`clear_followup_action()`**  
  Clears follow up action when it was executed.  
  Return type: `None`

- **`copy()`**  
  Creates a duplicate of this tracker  
  Return type: `DialogueStateTracker`

- **`current_slot_values()`**  
  Return the currently set values of the slots  
  Return type: `Dict[str, Any]`

- **`current_state(event_verbosity=<EventVerbosity.NONE: 1>)`**  
  Return the current tracker state as an object.  
  Return type: `Dict[str, Any]`

- **`events_after_latest_restart()`**  
  Return a list of events after the most recent restart.  
  Return type: `List[Event]`

- **`export_stories(e2e=False, include_source=False)`**  
  Dump the tracker as a story in the Rasa Core story format.  
  Returns the dumped tracker as a string.  
  Return type: `str`

- **`export_stories_to_file(export_path='debug.md')`**  
  Dump the tracker as a story to a file.  
  Return type: `None`

- **`from_dict(sender_id, events_as_dict, slots=None, max_event_history=None)`**  
  Create a tracker from dump.  
  The dump should be an array of dumped events. When restoring the tracker, these events will be replayed to recreate the state.  
  Return type: `DialogueStateTracker`

- **`generate_all_prior_trackers()`**  
  Returns a generator of the previous trackers of this tracker.  
  The resulting array is representing the trackers before each action.  
  Return type: `Generator[DialogueStateTracker, None, None]`

- **`get_last_event_for(event_type, action_names_to_exclude=None, skip=0)`**  
  Gets the last event of a given type which was actually applied.  
  Returns event which matched the query or None if no event matched.  
  Return type: `Optional[Event]`

- **`get_latest_entity_values(entity_type, entity_role=None, entity_group=None)`**  
  Get entity values found for the passed entity type and optional role and group in latest message.  
  Return type: `Iterator[str]`

- **`get_latest_input_channel()`**  
  Get the name of the input_channel of the latest UserUttered event  
  Return type: `Optional[str]`

- **`get_slot(key)`**  
  Retrieves the value of a slot.  
  Return type: `Optional[Any]`

- **`idx_after_latest_restart()`**  
  Return the idx of the most recent restart in the list of events.  
  If the conversation has not been restarted, `0` is returned.  
  Return type: `int`

- **`init_copy()`**  
  Creates a new state tracker with the same initial values.  
  Return type: `DialogueStateTracker`

- **`is_paused()`**  
  State whether the tracker is currently paused.  
  Return type: `bool`

- **`last_executed_action_has(name, skip=0)`**  
  Returns whether last ActionExecuted event had a specific name.  
  Return type: `bool`

- **`past_states(domain)`**  
  Generate the past states of this tracker based on the history.  
  Return type: `deque`

- **`recreate_from_dialogue(dialogue)`**  
  Use a serialised Dialogue to update the trackers state.  
  Return type: `None`

- **`reject_action(action_name)`**  
  Notify active form that it was rejected  
  Return type: `None`

- **`replay_events()`**  
  Update the tracker based on a list of events.  
  Return type: `None`

- **`set_form_validation(validate)`**  
  Toggle form validation  
  Return type: `None`

- **`set_latest_action_name(action_name)`**  
  Set latest action name and reset form validation and rejection parameters  
  Return type: `None`

- **`travel_back_in_time(target_time)`**  
  Creates a new tracker with a state at a specific timestamp.  
  Return type: `DialogueStateTracker`

- **`trigger_followup_action(action)`**  
  Triggers another action following the execution of the current.  
  Return type: `None`

- **`update(event, domain=None)`**  
  Modify the state of the tracker according to an `Event`.  
  Return type: `None`