# 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 behaviour, check out the docs on [Session configuration](https://legacy-docs-v1.rasa.com/1.7.2/core/domains/#session-config).

## Class: `rasa.core.trackers.DialogueStateTracker`  
Maintains the state of a conversation.

### 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.  
  **Return parameters:**  
  - **event_type** – The type of event you want to find.  
  - **action_names_to_exclude** – Events of type ActionExecuted which should be excluded from the results. Can be used to skip action_listen events.
  - **skip** – Skips n possible results before return an event.

**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 parameters:**  
  - **name** – Name of the event which should be matched.  
  - **skip** – Skips n possible results in between.
  **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.  This uses the state as is persisted in a `TrackerStore`.  If the tracker is blank before calling this method, the final state will be identical to the tracker from which the dialogue was created.  
 **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.  A new tracker will be created and all events previous to the passed time stamp will be replayed.  Events that occur exactly at the target time will be included.  
 **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`