Module API

py_trees_ros

ROS extensions, behaviours and utilities for py_trees.

py_trees_ros.actions

Behaviours for ROS actions.

class py_trees_ros.actions.ActionClient(action_type, action_name, action_goal, name=<Name.AUTO_GENERATED: 'AUTO_GENERATED'>, generate_feedback_message=None)

Bases: py_trees.behaviour.Behaviour

A generic action client interface. This simply sends a pre-configured goal to the action client.

Parameters:

• action_type (any) – spec type for the action (e.g. move_base_msgs.msg.MoveBaseAction)
• action_name (str) – where you can find the action topics & services (e.g. “bob/move_base”)
• action_goal (any) – pre-configured action goal (e.g. move_base_msgs.action.MoveBaseGoal())
• name (str, optional) – name of the behaviour defaults to lowercase class name
• generate_feedback_message (func, optional) – formatter for feedback messages, takes action_type.Feedback messages and returns strings, defaults to None

get_result_callback(future)

Handle result.

goal_response_callback(future)

Handle goal response, proceed to listen for the result if accepted.

initialise()

Reset the internal variables.

send_goal_request()

Send the goal and get a future back, but don’t do any spinning here to await the future result.

Returns:rclpy.task.Future

setup(**kwargs)

Setup the action client services and subscribers.

Parameters:

**kwargs (dict) – distribute arguments to this behaviour and in turn, all of it’s children

Raises:

• KeyError – if a ros2 node isn’t passed under the key ‘node’ in kwargs
• TimedOutError – if the action server could not be found

shutdown()

Clean up the action client when shutting down.

terminate(new_status)

If running and the current goal has not already succeeded, cancel it.

Parameters:new_status (Status) – the behaviour is transitioning to this new status

update()

Check only to see whether the underlying action server has succeeded, is running, or has cancelled/aborted for some reason and map these to the usual behaviour return states.

py_trees_ros.battery

Getting the most out of your battery.

class py_trees_ros.battery.ToBlackboard(name, topic_name='/battery/state', threshold=30.0)

Bases: py_trees_ros.subscribers.ToBlackboard

Subscribes to the battery message and writes battery data to the blackboard. Also adds a warning flag to the blackboard if the battery is low - note that it does some buffering against ping-pong problems so the warning doesn’t trigger on/off rapidly when close to the threshold.

When ticking, updates with RUNNING if it got no data, SUCCESS otherwise.

Blackboard Variables:

• battery (sensor_msgs.msg.BatteryState)[w]: the raw battery message
• battery_low_warning (bool)[w]: False if battery is ok, True if critically low

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the battery state topic
• threshold (float) – percentage level threshold for flagging as low (0-100)

update()

Call the parent to write the raw data to the blackboard and then check against the threshold to determine if the low warning flag should also be updated.

py_trees_ros.blackboard

This module provides the py_trees_ros.blackboard.Exchange class, a ROS wrapper around a Blackboard that permits introspection of either the entire board or a window onto a smaller part of the board over a ROS API via the py-trees-blackboard-watcher command line utility.

class py_trees_ros.blackboard.BlackboardView(node, topic_name, attrs)

Bases: object

Utility class that enables tracking and publishing of relevant parts of the blackboard for a user. This is used by the Exchange operator.

Parameters:

• topic_name (str) – name of the topic for the publisher
• attrs (???) –

class py_trees_ros.blackboard.BlackboardWatcher(callback=<function BlackboardWatcher.<lambda>>, namespace_hint=None)

Bases: object

The blackboard watcher sits on the other side of the exchange and is a useful mechanism from which to pull all or part of the blackboard contents. This is extremely useful for logging, but also for introspecting in the runtime for various uses (e.g. reporting out on the current state to a fleet server).

See also

py-trees-blackboard-watcher

close_connection()

Raises:

• NotReadyError – if setup not executed or it hitherto failed
• TimedOutError – if the services could not be reached

open_connection(variables, callback=None, executor=None)

First calls the exchange to get details on the connect the watcher is required to open and then initiates that tunnel. Note that this does some spinning waiting for the service call, so if the executor must be shared with other nodes (e.g. for testing) make sure you pass in your own executor.

Parameters:

• variables ([str]) – list of variables to listen for
• callback (func, optional) – method with a std_msgs/String argument, defaults to blackboard_contents_callback() in this class
• executor (Executor) –

Raises:

• NotReadyError – if setup not executed or it hitherto failed
• ServiceError – if the service failed to respond
• TimedOutError – if the services could not be reached

request_list_variables()

Request of the blackboard a list of it’s variables.

Returns:Future

setup(timeout_sec)

Parameters:

timeout_sec (float) – time (s) to wait (use common.Duration.INFINITE to block indefinitely)

Raises:

• NotFoundError – if no services were found
• MultipleFoundError – if multiple services were found

shutdown()

Perform any ros-specific shutdown.

class py_trees_ros.blackboard.Exchange

Bases: object

Establishes ros communications around a Blackboard that enable users to introspect or watch relevant parts of the blackboard.

ROS Publishers:

• ~/blackboard (std_msgs.msg.String)
  • streams (string form) the contents of the entire blackboard as it updates

ROS Services:

• ~/get_blackboard_variables (py_trees_msgs.srv.GetBlackboardVariables)
  • list all the blackboard variable names (not values)
• ~/open_blackboard_watcher (py_trees_msgs.srv.OpenBlackboardWatcher)
  • request a publisher to stream a part of the blackboard contents
• ~/close_blackboard_watcher (py_trees_msgs.srv.CloseBlackboardWatcher)
  • close a previously opened watcher

Watching could be more simply enabled by just providing a get style service on a particular variable(s), however that would introduce an asynchronous interrupt on the library’s usage and subsequently, locking. Instead, a watcher service requests for a stream, i.e. a publisher to be created for private use that streams only a subsection of the blackboard to the user. Additional services are provided for closing the stream and listing the variables on the blackboard.

See also

BehaviourTree (in which it is used) and py-trees-blackboard-watcher (working with the watchers).

publish_blackboard(unused_tree=None)

Lazy string publishing of the blackboard (the contents of the blackboard can be of many and varied types, so string form is the only way to transmit this across a ros message) on the ~blackboard topic.

Typically you would call this from a tree custodian (e.g. py_trees_ros.trees.BehaviourTree) after each and every tick.

Note

Lazy: it will only do the relevant string processing if there are subscribers present.

Parameters:unused_tree (any) – if used as a post_tick_handler, needs the argument, but nonetheless, gets unused

setup(node)

This is where the ros initialisation of publishers and services happens. It is kept outside of the constructor for the same reasons that the familiar py_trees setup() method has - to enable construction of behaviours and trees offline (away from their execution environment) so that dot graphs and other visualisations of the tree can be created.

Parameters:node (Node) – node to hook ros communications on

Examples

It is expected that users will use this in their own customised tree custodian:

class MyTreeManager(py_trees.trees.BehaviourTree):

    def __init__(self):
        pass

    def setup(self, timeout):
        super(MyTreeManager, self).setup(timeout)
        self.exchange = py_trees_ros.blackboard.Exchange()
        self.exchange.setup(timeout)

See also

This method is called in the way illustrated above in BehaviourTree.

py_trees_ros.conversions

Converter methods for transferring information back and forth between py_trees objects and ros messages.

py_trees_ros.conversions.behaviour_to_msg(behaviour)

Convert a behaviour to a message.

Parameters:behaviour (py_trees.behaviour.Behaviour) – behaviour to convert Returns:a ros message representation of a behaviour Return type:py_trees_ros_interfaces.msg.Behaviour

py_trees_ros.conversions.behaviour_type_to_msg_constant(behaviour)

Convert a behaviour class type to a message constant.

Parameters:behaviour (py_trees.behaviour.Behaviour) – investigate the type of this behaviour Returns:from the type constants in py_trees_ros_interfaces.msg.Behaviour Return type:uint8

py_trees_ros.conversions.blackbox_enum_to_msg_constant(blackbox_level)

Convert a blackbox level enum to a message constant.

Parameters:blackbox_level (BlackboxLevel) – blackbox level of a behaviour Returns:from the type constants in py_trees_ros_interfaces.msg.Behaviour Return type:uint8

py_trees_ros.conversions.msg_constant_to_behaviour_type(value)

Convert one of the behaviour type constants in a Behaviour message to a type.

Parameters:(obj (value) – int`: see the message definition for details Returns:a behaviour class type (e.g. py_trees.composites.Sequence) Raises:TypeError – if the message type is unrecognised

py_trees_ros.conversions.msg_constant_to_blackbox_level_enum(value)

Convert one of the blackbox level constants in a Behaviour message to a py_trees status enum.

Parameters:(obj (value) – int`: see the message definition for details Returns:a py_trees blackbox level Return type:py_trees.common.BlackBoxLevel Raises:TypeError – if the status type is unrecognised

py_trees_ros.conversions.msg_constant_to_status_enum(value)

Convert one of the status constants in a Behaviour message to a py_trees status enum.

Parameters:(obj (value) – int`: see the message definition for details Returns:a py_trees status Return type:Status Raises:TypeError – if the status type is unrecognised

py_trees_ros.conversions.msg_to_behaviour(msg)

Convert behaviour message to a py_trees behaviour. This doesn’t completely recreate the original behaviour (doesn’t have any of the custom state), but allows the user to compose a tree that can be utilised for debugging or visualisation applications.

Parameters:msg (py_trees_ros_interfaces.msg.Behaviour) – a ros message representation of a behaviour Returns:converted, skeleton of the original behaviour Return type:py_trees.behaviour.Behaviour

py_trees_ros.conversions.msg_to_uuid4(msg)

Convert a uuid4 python object to a ros unique identifier, UUID type.

Parameters:msg (unique_identifier_msgs.msg.UUID) – the ros message type Returns:the behaviour’s uuid, python style Return type:uuid.UUID

py_trees_ros.conversions.rclpy_duration_to_float(duration)

Convert a ros2 duration (seconds/nanoseconds) to a float.

Parameters:time (rclpy.time.Duration) – time to convert Return type:float

py_trees_ros.conversions.rclpy_time_to_float(time)

Convert a ros2 time (seconds/nanoseconds) to a float.

Parameters:time (rclpy.time.Time) – time to convert Return type:float

py_trees_ros.conversions.status_enum_to_msg_constant(status)

Convert a status to a message constant.

Parameters:status (Status) – status enum of a behaviour Returns:from the status constants in py_trees_ros_interfaces.msg.Behaviour Return type:uint8

py_trees_ros.conversions.uuid4_to_msg(uuid4=UUID('f161ea5c-9a90-496d-af0c-d8417a509f23'))

Convert a uuid4 python object to a ros unique identifier, UUID type.

Parameters:uuid4 (uuid.UUID) – unique identifier to convert, defaults to auto-generated uuid4 Returns:the ros message type Return type:unique_identifier_msgs.msg.UUID

py_trees_ros.subscribers

ROS subscribers are asynchronous communication handles whilst py_trees are by their nature synchronous. They tick, pause, then tick again and provide an assumption that only one behaviour or function is running at any single moment. Firing off a subscriber callback in the middle of that synchronicity to write to a blackboard would break this assumption.

To get around that, subscriber behaviours run the ros callbacks in a background thread and constrain locking and a local cache inside the behaviour. Only in the update function is a cached variable unlocked and then permitted to be used or written to the blackboard.

class py_trees_ros.subscribers.CheckData(name='Check Data', topic_name='/foo', topic_type=None, qos_profile=<Mock name='mock.qos.QoSProfile()' id='140624793538688'>, variable_name='bar', expected_value=None, fail_if_no_data=False, fail_if_bad_comparison=False, comparison_operator=<built-in function eq>, clearing_policy=<ClearingPolicy.ON_INITIALISE: 1>)

Bases: py_trees_ros.subscribers.Handler

Check a subscriber to see if it has received data.

It optionally checks whether that data, or part of it has a specific value.

Usage Patterns

Sequence Guard: RUNNING until there is a successful comparison

• fail_if_no_data=False
• fail_if_bad_comparison=False

Selector Priority Chooser: FAILURE until there is a successful comparison

• fail_if_no_data=True
• fail_if_bad_comparison=True

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the topic to connect to
• topic_type (any) – class of the message type (e.g. std_msgs.msg.String)
• qos_profile (bool) – qos profile for the subscriber
• variable_name (str) – name of the variable to check
• expected_value (any) – expected value of the variable
• fail_if_no_data (bool) – FAILURE instead of RUNNING if there is no data yet
• fail_if_bad_comparison (bool) – FAILURE instead of RUNNING if comparison failed
• comparison_operator (func) – one from the python operator module
• clearing_policy (ClearingPolicy) – when to clear the data

Tip

Prefer ToBlackboard and the various blackboard checking behaviours instead. It will provide you with better introspection capability and less complex behaviour construction to manage.

update()

Handles all the logic for determining what result should go back.

Returns:depending on the checking results Return type:Status

class py_trees_ros.subscribers.EventToBlackboard(name='Event to Blackboard', topic_name='/event', qos_profile=<Mock name='mock.qos.QoSProfile()' id='140624793538688'>, variable_name='event')

Bases: py_trees_ros.subscribers.Handler

Listen for events (std_msgs.msg.Empty) on a subscriber and writes the result to the blackboard.

This will write True if at least one message was received, False otherwise to a bool. This can then be consumed by the tree’s tick. No need to clean up, it will write anew on the next tick.

Tip

Ideally you need this at the very highest part of the tree so that it gets triggered every time - once this happens, then the rest of the behaviour tree can utilise the variables.

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the topic to connect to
• qos_profile (bool) – qos profile for the subscriber
• variable_name (str) – name to write the boolean result on the blackboard

update()

Check for data and write to the board.

class py_trees_ros.subscribers.Handler(name='Subscriber Handler', topic_name='/foo', topic_type=None, qos_profile=<Mock name='mock.qos.qos_profile_default' id='140624793443408'>, clearing_policy=<ClearingPolicy.ON_INITIALISE: 1>)

Bases: py_trees.behaviour.Behaviour

Warning

Do not use - it will always return INVALID. Subclass it to create a functional behaviour.

Not intended for direct use, as this just absorbs the mechanics of setting up a subscriber for inheritance by user-defined behaviour classes. There are several options for the mechanism of clearing the data so that a new result can be processed.

Always Look for New Data

This will clear any currently stored data upon entry into the behaviour (i.e. when initialise() is called). This is useful for a behaviour in a sequence that is looking to start fresh as it is about to tick and be in a RUNNING state until new data arrives.

Look for New Data only after SUCCESS

This will clear any currently stored data as soon as the behaviour returns SUCCESS. This is useful for catching new triggers/events from things like buttons where you don’t want to miss things even though you may not actually be ticking.

Use the Latest Data

Even if this data was received before entry into the behaviour. In this case initialise() does not do anything with the currently stored data. Useful as a blocking behaviour to wait on some some topic having been initialised with some data (e.g. CameraInfo).

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the topic to connect to
• topic_type (any) – class of the message type (e.g. std_msgs.msg.String)
• qos_profile (bool) – qos profile for the subscriber
• clearing_policy (ClearingPolicy) – when to clear the data

initialise()

If the clearing policy is set to ON_INITIALISE it will clear the internally saved message, otherwise it does nothing.

setup(**kwargs)

Initialises the subscriber.

Parameters:**kwargs (dict) – distribute arguments to this behaviour and in turn, all of it’s children Raises:KeyError – if a ros2 node isn’t passed under the key ‘node’ in kwargs

class py_trees_ros.subscribers.ToBlackboard(name='ToBlackboard', topic_name='chatter', topic_type=None, qos_profile=<Mock name='mock.qos.QoSProfile()' id='140624793538688'>, blackboard_variables={'chatter': None}, initialise_variables={}, clearing_policy=<ClearingPolicy.ON_INITIALISE: 1>)

Bases: py_trees_ros.subscribers.Handler

Saves the latest message to the blackboard and immediately returns success. If no data has yet been received, this behaviour blocks (i.e. returns RUNNING).

Typically this will save the entire message, however sub fields can be designated, in which case they will write to the specified keys.

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the topic to connect to
• topic_type (any) – class of the message type (e.g. std_msgs.msg.String)
• qos_profile (bool) – qos profile for the subscriber
• blackboard_variables (dict) – blackboard variable string or dict {names (keys) - message subfields (values)}, use a value of None to indicate the entire message
• initialise_variables (bool) – initialise the blackboard variables to some defaults
• clearing_policy (ClearingPolicy) – when to clear the data

Examples

To capture an entire message:

chatter_to_blackboard = ToBlackboard(topic_name="chatter",
                                     topic_type=std_msgs.msg.String,
                                     blackboard_variables = {'chatter': None}
                                     )

or to get rid of the annoying sub-data field in std_msgs/String:

chatter_to_blackboard = ToBlackboard(topic_name="chatter",
                                     topic_type=std_msgs.msg.String,
                                     blackboard_variables = {'chatter': 'data'}
                                     )

combinations of multiple entities inside the message can also be saved:

blackboard_variables={"pose_with_covariance_stamped": None, "pose": "pose.pose"}

update()

Writes the data (if available) to the blackboard.

Returns:RUNNING (no data) or SUCCESS Return type:Status

class py_trees_ros.subscribers.WaitForData(name='Wait For Data', topic_name='chatter', topic_type=None, qos_profile=<Mock name='mock.qos.QoSProfile()' id='140624793538688'>, clearing_policy=<ClearingPolicy.ON_INITIALISE: 1>)

Bases: py_trees_ros.subscribers.Handler

Waits for a subscriber’s callback to be triggered. This doesn’t care about the actual data, just whether it arrived or not, so is useful for catching triggers (std_msgs/Empty messages) or blocking (in the behaviour sense) until some data has arrived (e.g. camera configuration). There are two use cases:

Usage Patterns

Got Something, Sometime

• clearing_policy == NEVER

Don’t care when data arrived, just that it arrived. This could be for something like a map topic, or a configuration that you need to block. Once it returns SUCCESS, it will always return SUCCESS.

Wating for the Next Thing, Starting From Now

• clearing_policy == ON_INTIALISE

Useful as a gaurd at the start of a sequence, that is waiting for an event to trigger after the sequence has started (i.e. been initialised).

Wating for the Next Thing, Starting from the Last

• clearing_policy == ON_SUCCESS

Useful as a guard watching for an event that could have come in anytime, but for which we do with to reset (and subsequently look for the next event). e.g. button events.

Parameters:

• name (str) – name of the behaviour
• topic_name (str) – name of the topic to connect to
• topic_type (any) – class of the message type (e.g. std_msgs.msg.String)
• qos_profile (bool) – qos profile for the subscriber
• clearing_policy (ClearingPolicy) – when to clear the data

update()

Returns:RUNNING (no data) or SUCCESS Return type:Status

py_trees_ros.trees

The py_trees_ros.trees.BehaviourTree class extends the core py_trees.trees.BehaviourTree class with a ROS publisher that publishes the initial and updated snapshots of the tree whenever the tree changes.

‘Change’ is defined by deletion or insertion of behaviours into the tree or the status of any behaviour in the tree changing from tick to tick.

class py_trees_ros.trees.BehaviourTree(root, unicode_tree_debug=False)

Bases: py_trees.trees.BehaviourTree

Extend the py_trees.trees.BehaviourTree class with a few bells and whistles for ROS:

• ros publishers that serialises a snapshot of the tree for viewing/logging
• a blackboard exchange with introspection and watcher services

ROS Publishers:

• ~/snapshots (py_trees_msgs.msg.BehaviourTree)

See also

It also exposes publishers and services from the blackboard exchange in it’s private namespace. Refer to Exchange for details.

Parameters:

• root (Behaviour) – root node of the tree
• unicode_tree_debug (bool, optional) – print to console the visited ascii tree after every tick

Raises:

AssertionError – if incoming root variable is not the correct type

setup(timeout=<Duration.INFINITE: inf>)

Setup the publishers, exechange and add ros-relevant pre/post tick handlers to the tree. Ultimately relays this call down to all the behaviours in the tree.

Parameters:

timeout (float) – time (s) to wait (use common.Duration.INFINITE to block indefinitely)

Raises:

• rclpy.exceptions.NotInitializedException – rclpy not yet initialised
• Exception – be ready to catch if any of the behaviours raise an exception

shutdown()

Cleanly shut down rclpy timers and nodes.

tick_tock(period_ms, number_of_iterations=-1, pre_tick_handler=None, post_tick_handler=None)

Tick continuously at the period specified.

This is a re-implementation of the tick_tock() tick_tock that takes advantage of the rclpy timers so callbacks are interleaved inbetween rclpy callbacks (keeps everything synchronous so no need for locks).

Parameters:

• period_ms (float) – sleep this much between ticks (milliseconds)
• number_of_iterations (int) – number of iterations to tick-tock
• pre_tick_handler (func) – function to execute before ticking
• post_tick_handler (func) – function to execute after ticking

class py_trees_ros.trees.Watcher(namespace_hint, mode=<WatcherMode.ASCII_SNAPSHOT: 'ASCII_SNAPSHOT'>)

Bases: object

The tree watcher sits on the other side of a running BehaviourTree and is a useful mechanism for quick introspection of it’s current state.

Parameters:

• namespace_hint (str) – (optionally) used to locate the blackboard if there exists more than one
• mode (WatcherMode) – viewing mode for the watcher

See also

py_trees_ros.programs.tree_watcher

callback_snapshot(msg)

Formats the string message coming in.

Args

msg (py_trees_ros_interfaces.msg.BehaviourTree):serialised snapshot

setup()

Parameters:

timeout (float) – time to wait (0.0 is blocking forever)

Raises:

• NotFoundError – if no services were found
• MultipleFoundError – if multiple services were found

class py_trees_ros.trees.WatcherMode

Bases: enum.Enum

An enumerator specifying the view mode for the watcher

ASCII_SNAPSHOT = 'ASCII_SNAPSHOT'

Print an ascii art view of the behaviour tree’s current state after the last tick

ASCII_TREE = 'ASCII_TREE'

Print an ascii art representation of the static tree (sans visited path/status/feedback messages).

DOT_TREE = 'DOT_TREE'

Render with the dot graph representation of the static tree (using an application or text to console).

py_trees_ros.utilities

Assorted utility functions.

class py_trees_ros.utilities.Publishers(node, publisher_details, introspection_topic_name='publishers')

Bases: object

Utility class that groups the publishers together in one convenient structure.

Parameters:(obj (publisher_details) – tuple): list of (str, str, bool, int) tuples representing (unique_name, topic_name, publisher_type, latched) specifications for creating publishers

Examples

Convert the incoming list of specifications into proper variables of this class.

publishers = py_trees.utilities.Publishers(
    [
        ('foo', ~/foo', std_msgs.String, True, 5),
        ('bar', /foo/bar', std_msgs.String, False, 5),
        ('foobar', '/foo/bar', std_msgs.String, False, 5),
    ]
)

class py_trees_ros.utilities.Subscribers(node, subscriber_details, introspection_topic_name='subscribers')

Bases: object

Utility class that groups the publishers together in one convenient structure.

Parameters:(obj (subscriber_details) – tuple): list of (str, str, bool, func) tuples representing (unique_name, topic_name, subscriber_type, latched, callback) specifications for creating subscribers

Examples

Convert the incoming list of specifications into proper variables of this class.

subscribers = py_trees.utilities.Subscribers(
    [
        ('foo', ~/foo', std_msgs.String, True, foo),
        ('bar', /foo/bar', std_msgs.String, False, self.foo),
        ('foobar', '/foo/bar', std_msgs.String, False, foo.bar),
    ]
)

py_trees_ros.utilities.basename(name)

Generate the basename from a ros name.

Parameters:name (str) – ros name Returns:name stripped up until the last slash or tilde character. Return type:str

Examples

basename("~dude")
# 'dude'
basename("/gang/dude")
# 'dude'

py_trees_ros.utilities.create_anonymous_node_name(node_name='node')

Creates an anonoymous node name by adding a suffix created from a monotonic timestamp, sans the decimal.

Returns:the unique, anonymous node name Return type:str

py_trees_ros.utilities.find_service(node, service_type, namespace=None)

Discover a service of the specified type and if necessary, under the specified namespace.

Parameters:

• node (Node) – nodes have the discovery methods
• service_type (str) – primary lookup hint
• namespace (str) – secondary lookup hint

Returns:

fully expanded the service name

Return type:

str

Raises:

• NotFoundError – if no services were found
• MultipleFoundError – if multiple services were found

py_trees_ros.utilities.find_topic(node, topic_type, namespace=None)

Discover a topic of the specified type and if necessary, under the specified namespace.

Parameters:

• node (Node) – nodes have the discovery methods
• topic_type (str) – primary lookup hint
• namespace (str) – secondary lookup hint

Returns:

fully expanded the service name

Return type:

str

Raises:

• NotFoundError – if no services were found
• MultipleFoundError – if multiple services were found

py_trees_ros.utilities.get_py_trees_home()

Find the default home directory used for logging, bagging and other esoterica.

py_trees_ros.utilities.qos_profile_latched_topic()

Convenience retrieval for a latched topic (publisher / subscriber)

py_trees_ros.utilities.resolve_name(node, name)

Convenience function for getting the resolved name (similar to ‘publisher.resolved_name’ in ROS1).

Parameters:

• node (rclpy.node.Node) – the node, namespace it should be relevant to
• (obj (name) – str): topic or service name

Note

This entirely depends on the user providing the relevant node, name pair.

py_trees_ros.visitors

ROS Visitors are entities that can be passed to a ROS 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).

Warning

Visitors should not modify the behaviours they visit.

See also

The base interface and core visitors in py_trees.visitors

class py_trees_ros.visitors.TreeToMsgVisitor

Bases: py_trees.visitors.VisitorBase

Visits the entire tree and gathers all behaviours as messages for the tree logging publishers.

Variables:tree (py_trees_msgs.msg.BehaviourTree) – tree representation in message form

initialise()

Initialise and stamp a py_trees_msgs.msg.BehaviourTree instance.

run(behaviour)

Convert the behaviour into a message and append to the tree.

Parameters:behaviour (Behaviour) – behaviour to convert

py_trees_ros.programs

Entry points to the programs (tools and utilities).

py_trees_ros.programs.blackboard_watcher

Open up a window onto the blackboard!

Examples:

$ py-trees-blackboard-watcher 
$ py-trees-blackboard-watcher --list-variables
$ py-trees-blackboard-watcher access_point odom/pose/pose/position

usage: py-trees-blackboard-watcher [-h] [-l] [-n [NAMESPACE]] ...

Positional Arguments

variables

space separated list of blackboard variables to watch Default: []

Named Arguments

-l, --list-variables
	list the blackboard variables
-n, --namespace
	namespace of blackboard services (if there should be more than one blackboard)

Example interaction with the services of an py_trees_ros.blackboard.Exchange:

py_trees_ros.programs.blackboard_watcher.echo_blackboard_contents(contents)

Parameters:contents (str) – blackboard contents

Note

The string comes pre-formatted with bash color identifiers and newlines. This is currently not especially good for anything other than debugging.

py_trees_ros.programs.blackboard_watcher.main(command_line_args=['-T', '-W', '-b', 'readthedocs', '-d', '_build/doctrees-readthedocs', '-D', 'language=en', '.', '_build/html'])

Entry point for the blackboard watcher script.

py_trees_ros.programs.tree_watcher

Open up a window onto the behaviour tree!

Print static or dynamic (snapshot) unicode art views of the tree on the console or render a dot graph (static view only). Use the namespace argument to select from trees when there are multiple available.

Examples:

$ py-trees-tree-watcher 
$ py-trees-tree-watcher --unicode-tree
$ py-trees-tree-watcher --dot-tree
$ py-trees-tree-watcher --namespace=foo --unicode-tree

usage: py-trees-tree-watcher [-h] [-n [NAMESPACE]] [-s | -t | -d]

Named Arguments

-n, --namespace
	namespace of pytree communications (if there should be more than one tree active)
-s, --snapshot	print a live snapshot of the tree state as unicode art on your console
-t, --tree	print the tree structure as unicode art on your console
-d, --dot-tree	render the tree structure as a dot graph

Command line utility to interact with a running BehaviourTree instance. Print the tree structure or a live snapshot of the tree state as unicode art on your console, view tick statistics as a stream or display the tree as a dot graph.

py_trees_ros.programs.tree_watcher.echo_blackboard_contents(contents)

Parameters:contents (str) – blackboard contents

Note

The string comes pre-formatted with bash color identifiers and newlines. This is currently not especially good for anything other than debugging.

py_trees_ros.programs.tree_watcher.main()

Entry point for the tree watcher script.