# 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/1.8.0/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.

### `applied_events`()  
Returns all actions that should be applied - w/o reverted events.

**Return type**  
`List`

### `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`](https://legacy-docs-v1.rasa.com/1.8.0/api/tracker/#rasa.core.trackers.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`

### _classmethod_`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`](https://legacy-docs-v1.rasa.com/1.8.0/api/tracker/#rasa.core.trackers.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`](https://legacy-docs-v1.rasa.com/1.8.0/api/tracker/#rasa.core.trackers.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.

**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.

**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.

If you are only interested in the first entity of a given type use next(tracker.get_latest_entity_values(“my_entity_name”), None). If no entity is found None is the default result.

**Parameters**  
- **entity_type** – the entity type of interest
- **entity_role** – optional entity role of interest
- **entity_group** – optional entity group of interest

**Returns**  
Entity values.

**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`](https://legacy-docs-v1.rasa.com/1.8.0/api/tracker/#rasa.core.trackers.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.

**Parameters**  
- **name** – Name of the event which should be matched.
- **skip** – Skips n possible results in between.

**Returns**  
True if last executed action had name name, otherwise False.

**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`](https://legacy-docs-v1.rasa.com/1.8.0/api/tracker/#rasa.core.trackers.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`  
  
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