# Tracker [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#tracker "Permalink to this headline")

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/1.9.4/core/domains/#session-config).

_class_`rasa.core.trackers.``DialogueStateTracker`( _sender_id_, _slots_, _max_event_history=None_, _sender_source=None_) [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#rasa.core.trackers.DialogueStateTracker "Permalink to this definition")

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`() [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#rasa.core.trackers.DialogueStateTracker.applied_events "Permalink to this definition")

Returns all actions that should be applied - w/o reverted events.

Return type

`List`[`Event`]

`as_dialogue`() [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#rasa.core.trackers.DialogueStateTracker.as_dialogue "Permalink to this definition")

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_) [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#rasa.core.trackers.DialogueStateTracker.change_form_to "Permalink to this definition")

Activate or deactivate a form

Return type

`None`

`clear_followup_action`() [¶](https://legacy-docs-v1.rasa.com/1.9.4/api/tracker/#rasa.core.trackers.DialogueStateTracker.clear_followup_action "Permalink to this definition")

Clears follow up action when it was executed.

Return type

`None`