py_trees.visitors module

Visiting rights to behaviours.

Visitors are entities that can be passed to a tree implementation (e.g. BehaviourTree) and used to either visit each and every behaviour in the tree, or visit behaviours as the tree is traversed in an executing tick. At each behaviour, the visitor runs its own method on the behaviour to do as it wishes - logging, introspecting, etc.

Warning

Visitors should not modify the behaviours they visit.

class py_trees.visitors.DebugVisitor

Bases: VisitorBase

Picks up and logs feedback messages and the behaviour’s status.

Logging is done with the behaviour’s logger.

run(behaviour: Behaviour) → None

Log behaviour information on the debug channel.

Args:

behaviour: behaviour being visited.

class py_trees.visitors.DisplaySnapshotVisitor(display_only_visited_behaviours: bool = False, display_blackboard: bool = False, display_activity_stream: bool = False)

Bases: SnapshotVisitor

Visit the tree, capturing the visited path, it’s changes since the last tick.

Additionally print the snapshot to console.

Args:

display_only_visited_behaviours: useful for cropping the unvisited part of a large tree display_blackboard: print to the console the relevant part of the blackboard associated with

behaviours on the visited path

display_activity_stream: print to the console a log of the activity on the blackboard

over the last tick

finalise() → None

Print a summary on stdout after all behaviours have been visited.

initialise() → None

Reset and initialise all variables.

run(behaviour: Behaviour) → None

Track the root of the tree and run SnapshotVisitor.

Args:

behaviour: behaviour being visited.

class py_trees.visitors.SnapshotVisitor

Bases: VisitorBase

Creates a snapshot of the tree state (behaviour status’ only).

Visits the ticked part of a tree, checking off the status against the set of status results recorded in the previous tick. If there has been a change, it flags it. This is useful for determining when to trigger, e.g. logging.

Attributes:

changed (Bool): flagged if there is a difference in the visited path or

Status of any behaviour on the path

visited (dict): dictionary of behaviour id (uuid.UUID) and status

(Status) pairs from the current tick

previously_visited (dict): dictionary of behaviour id (uuid.UUID)

and status (Status) pairs from the previous tick

running_nodes([uuid.UUID]): list of id’s for behaviours which were traversed in the current tick previously_running_nodes([uuid.UUID]): list of id’s for behaviours which were traversed in the last tick visited_blackboard_ids(typing.Set[uuid.UUID]): blackboard client id’s on the visited path visited_blackboard_keys(typing.Set[str]): blackboard variable keys on the visited path

See also

The py-trees-demo-logging-program program demonstrates use of this visitor to trigger logging of a tree serialisation.

initialise() → None

Store the last snapshot for comparison with the next incoming snapshot.

This should get called before a tree ticks.

run(behaviour: Behaviour) → None

Catch the id, status and store it.

Additionally add it to the running list if it is RUNNING.

Args:

behaviour: behaviour that is ticking

class py_trees.visitors.VisitorBase(full: bool = False)

Bases: object

Parent template for visitor types.

Visitors are primarily designed to work with BehaviourTree but they can be used in the same way for other tree custodian implementations.

Args:

full: flag to indicate whether it should be used to visit only traversed nodes or the entire tree

Attributes:

full: flag to indicate whether it should be used to visit only traversed nodes or the entire tree

finalise() → None

Override if any work needs to be performed after ticks (i.e. showing data).

initialise() → None

Override if any resetting of variables needs to be performed between ticks (i.e. visitations).

run(behaviour: Behaviour) → None

Converse with the behaviour.

This method gets run as each behaviour is ticked. Override it to perform some activity - e.g. introspect the behaviour to store/process logging data for visualisations.

Args:

behaviour (Behaviour): behaviour that is ticking