Demos

py-trees-demo-action-behaviour

Demonstrates the characteristics of a typical ‘action’ behaviour.

• Mocks an external process and connects to it in the setup() method
• Kickstarts new goals with the external process in the initialise() method
• Monitors the ongoing goal status in the update() method
• Determines RUNNING/SUCCESS pending feedback from the external process

usage: py-trees-demo-action-behaviour [-h]

class py_trees.demos.action.Action(name='Action')

Bases: py_trees.behaviour.Behaviour

Connects to a subprocess to initiate a goal, and monitors the progress of that goal at each tick until the goal is completed, at which time the behaviour itself returns with success or failure (depending on success or failure of the goal itself).

This is typical of a behaviour that is connected to an external process responsible for driving hardware, conducting a plan, or a long running processing pipeline (e.g. planning/vision).

Key point - this behaviour itself should not be doing any work!

__init__(name='Action')

Default construction.

initialise()

Reset a counter variable.

setup()

No delayed initialisation required for this example.

terminate(new_status)

Nothing to clean up in this example.

update()

Increment the counter and decide upon a new status result for the behaviour.

py_trees.demos.action.main()

Entry point for the demo script.

py_trees.demos.action.planning(pipe_connection)

Emulates an external process which might accept long running planning jobs.

py_trees/demos/action.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.action
   :func: command_line_argument_parser
   :prog: py-trees-demo-action-behaviour

.. image:: images/action.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import atexit
import multiprocessing
import py_trees.common
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Demonstrates the characteristics of a typical 'action' behaviour.\n"
    content += "\n"
    content += "* Mocks an external process and connects to it in the setup() method\n"
    content += "* Kickstarts new goals with the external process in the initialise() method\n"
    content += "* Monitors the ongoing goal status in the update() method\n"
    content += "* Determines RUNNING/SUCCESS pending feedback from the external process\n"

    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Action Behaviour".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    return argparse.ArgumentParser(description=description(),
                                   epilog=epilog(),
                                   formatter_class=argparse.RawDescriptionHelpFormatter,
                                   )


def planning(pipe_connection):
    """
    Emulates an external process which might accept long running planning jobs.
    """
    idle = True
    percentage_complete = 0
    try:
        while(True):
            if pipe_connection.poll():
                pipe_connection.recv()
                percentage_complete = 0
                idle = False
            if not idle:
                percentage_complete += 10
                pipe_connection.send([percentage_complete])
                if percentage_complete == 100:
                    idle = True
            time.sleep(0.5)
    except KeyboardInterrupt:
        pass


class Action(py_trees.behaviour.Behaviour):
    """
    Connects to a subprocess to initiate a goal, and monitors the progress
    of that goal at each tick until the goal is completed, at which time
    the behaviour itself returns with success or failure (depending on
    success or failure of the goal itself).

    This is typical of a behaviour that is connected to an external process
    responsible for driving hardware, conducting a plan, or a long running
    processing pipeline (e.g. planning/vision).

    Key point - this behaviour itself should not be doing any work!
    """
    def __init__(self, name="Action"):
        """
        Default construction.
        """
        super(Action, self).__init__(name)
        self.logger.debug("%s.__init__()" % (self.__class__.__name__))

    def setup(self):
        """
        No delayed initialisation required for this example.
        """
        self.logger.debug("%s.setup()->connections to an external process" % (self.__class__.__name__))
        self.parent_connection, self.child_connection = multiprocessing.Pipe()
        self.planning = multiprocessing.Process(target=planning, args=(self.child_connection,))
        atexit.register(self.planning.terminate)
        self.planning.start()

    def initialise(self):
        """
        Reset a counter variable.
        """
        self.logger.debug("%s.initialise()->sending new goal" % (self.__class__.__name__))
        self.parent_connection.send(['new goal'])
        self.percentage_completion = 0

    def update(self):
        """
        Increment the counter and decide upon a new status result for the behaviour.
        """
        new_status = py_trees.common.Status.RUNNING
        if self.parent_connection.poll():
            self.percentage_completion = self.parent_connection.recv().pop()
            if self.percentage_completion == 100:
                new_status = py_trees.common.Status.SUCCESS
        if new_status == py_trees.common.Status.SUCCESS:
            self.feedback_message = "Processing finished"
            self.logger.debug("%s.update()[%s->%s][%s]" % (self.__class__.__name__, self.status, new_status, self.feedback_message))
        else:
            self.feedback_message = "{0}%".format(self.percentage_completion)
            self.logger.debug("%s.update()[%s][%s]" % (self.__class__.__name__, self.status, self.feedback_message))
        return new_status

    def terminate(self, new_status):
        """
        Nothing to clean up in this example.
        """
        self.logger.debug("%s.terminate()[%s->%s]" % (self.__class__.__name__, self.status, new_status))


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    command_line_argument_parser().parse_args()

    print(description())

    py_trees.logging.level = py_trees.logging.Level.DEBUG

    action = Action()
    action.setup()
    try:
        for unused_i in range(0, 12):
            action.tick_once()
            time.sleep(0.5)
        print("\n")
    except KeyboardInterrupt:
        pass

py-trees-demo-behaviour-lifecycle

Demonstrates a typical day in the life of a behaviour.

This behaviour will count from 1 to 3 and then reset and repeat. As it does so, it logs and displays the methods as they are called - construction, setup, initialisation, ticking and termination.

usage: py-trees-demo-behaviour-lifecycle [-h]

class py_trees.demos.lifecycle.Counter(name='Counter')

Bases: py_trees.behaviour.Behaviour

Simple counting behaviour that facilitates the demonstration of a behaviour in the demo behaviours lifecycle program.

• Increments a counter from zero at each tick
• Finishes with success if the counter reaches three
• Resets the counter in the initialise() method.

__init__(name='Counter')

Default construction.

initialise()

Reset a counter variable.

setup()

No delayed initialisation required for this example.

terminate(new_status)

Nothing to clean up in this example.

update()

Increment the counter and decide upon a new status result for the behaviour.

py_trees.demos.lifecycle.main()

Entry point for the demo script.

py_trees/demos/lifecycle.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.lifecycle
   :func: command_line_argument_parser
   :prog: py-trees-demo-behaviour-lifecycle

.. image:: images/lifecycle.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Demonstrates a typical day in the life of a behaviour.\n\n"
    content += "This behaviour will count from 1 to 3 and then reset and repeat. As it does\n"
    content += "so, it logs and displays the methods as they are called - construction, setup,\n"
    content += "initialisation, ticking and termination.\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Behaviour Lifecycle".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    return argparse.ArgumentParser(description=description(),
                                   epilog=epilog(),
                                   formatter_class=argparse.RawDescriptionHelpFormatter,
                                   )


class Counter(py_trees.behaviour.Behaviour):
    """
    Simple counting behaviour that facilitates the demonstration of a behaviour in
    the demo behaviours lifecycle program.

    * Increments a counter from zero at each tick
    * Finishes with success if the counter reaches three
    * Resets the counter in the initialise() method.
    """
    def __init__(self, name="Counter"):
        """
        Default construction.
        """
        super(Counter, self).__init__(name)
        self.logger.debug("%s.__init__()" % (self.__class__.__name__))

    def setup(self):
        """
        No delayed initialisation required for this example.
        """
        self.logger.debug("%s.setup()" % (self.__class__.__name__))

    def initialise(self):
        """
        Reset a counter variable.
        """
        self.logger.debug("%s.initialise()" % (self.__class__.__name__))
        self.counter = 0

    def update(self):
        """
        Increment the counter and decide upon a new status result for the behaviour.
        """
        self.counter += 1
        new_status = py_trees.common.Status.SUCCESS if self.counter == 3 else py_trees.common.Status.RUNNING
        if new_status == py_trees.common.Status.SUCCESS:
            self.feedback_message = "counting...{0} - phew, thats enough for today".format(self.counter)
        else:
            self.feedback_message = "still counting"
        self.logger.debug("%s.update()[%s->%s][%s]" % (self.__class__.__name__, self.status, new_status, self.feedback_message))
        return new_status

    def terminate(self, new_status):
        """
        Nothing to clean up in this example.
        """
        self.logger.debug("%s.terminate()[%s->%s]" % (self.__class__.__name__, self.status, new_status))


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    command_line_argument_parser().parse_args()

    print(description())

    py_trees.logging.level = py_trees.logging.Level.DEBUG

    counter = Counter()
    counter.setup()
    try:
        for unused_i in range(0, 7):
            counter.tick_once()
            time.sleep(0.5)
        print("\n")
    except KeyboardInterrupt:
        print("")
        pass

py-trees-demo-blackboard

Demonstrates usage of the blackboard and related behaviours.

A sequence is populated with a few behaviours that exercise reading and writing on the Blackboard in interesting ways.

usage: py-trees-demo-blackboard [-h] [-r | --render-with-blackboard-variables]

Named Arguments

-r, --render	render dot tree to file Default: False
--render-with-blackboard-variables
	render dot tree to file with blackboard variables Default: False

class py_trees.demos.blackboard.BlackboardWriter(name='Writer')

Bases: py_trees.behaviour.Behaviour

Custom writer that submits a more complicated variable to the blackboard.

__init__(name='Writer')

Initialize self. See help(type(self)) for accurate signature.

update()

Write a dictionary to the blackboard and return SUCCESS.

class py_trees.demos.blackboard.Nested

Bases: object

A more complex object to interact with on the blackboard.

__init__()

Initialize self. See help(type(self)) for accurate signature.

__str__()

Return str(self).

__weakref__

list of weak references to the object (if defined)

py_trees.demos.blackboard.main()

Entry point for the demo script.

py_trees/demos/blackboard.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.blackboard
   :func: command_line_argument_parser
   :prog: py-trees-demo-blackboard

.. graphviz:: dot/demo-blackboard.dot
   :align: center

.. image:: images/blackboard.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import sys

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Demonstrates usage of the blackboard and related behaviours.\n"
    content += "\n"
    content += "A sequence is populated with a few behaviours that exercise\n"
    content += "reading and writing on the Blackboard in interesting ways.\n"

    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Blackboard".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    render_group = parser.add_mutually_exclusive_group()
    render_group.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    render_group.add_argument(
        '--render-with-blackboard-variables',
        action='store_true',
        help='render dot tree to file with blackboard variables'
    )
    return parser


class Nested(object):
    """
    A more complex object to interact with on the blackboard.
    """
    def __init__(self):
        self.foo = "bar"

    def __str__(self):
        return str({"foo": self.foo})


class BlackboardWriter(py_trees.behaviour.Behaviour):
    """
    Custom writer that submits a more complicated variable to the blackboard.
    """
    def __init__(self, name="Writer"):
        super().__init__(name=name)
        self.blackboard.register_key(key="dude", read=True)
        self.blackboard.register_key(key="spaghetti", write=True)

        self.logger.debug("%s.__init__()" % (self.__class__.__name__))

    def update(self):
        """
        Write a dictionary to the blackboard and return :data:`~py_trees.common.Status.SUCCESS`.
        """
        self.logger.debug("%s.update()" % (self.__class__.__name__))
        try:
            unused = self.blackboard.dude
        except KeyError:
            pass
        try:
            unused = self.blackboard.dudette
        except AttributeError:
            pass
        try:
            self.blackboard.dudette = "Jane"
        except AttributeError:
            pass
        self.blackboard.spaghetti = {"type": "Carbonara", "quantity": 1}
        self.blackboard.spaghetti = {"type": "Gnocchi", "quantity": 2}
        try:
            self.blackboard.set("spaghetti", {"type": "Bolognese", "quantity": 3}, overwrite=False)
        except AttributeError:
            pass
        return py_trees.common.Status.SUCCESS


def create_root():
    root = py_trees.composites.Sequence("Blackboard Demo")
    set_blackboard_variable = py_trees.behaviours.SetBlackboardVariable(
        name="Set Nested", variable_name="nested", variable_value=Nested()
    )
    write_blackboard_variable = BlackboardWriter(name="Writer")
    check_blackboard_variable = py_trees.behaviours.CheckBlackboardVariableValue(
        name="Check Nested Foo", variable_name="nested.foo", expected_value="bar"
    )
    root.add_children([set_blackboard_variable, write_blackboard_variable, check_blackboard_variable])
    return root

##############################################################################
# Main
##############################################################################


def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    print(description())
    py_trees.logging.level = py_trees.logging.Level.DEBUG
    py_trees.blackboard.Blackboard.enable_activity_stream(maximum_size=100)
    standalone_blackboard = py_trees.blackboard.BlackboardClient(
        name="Standalone Blackboard Client",
        write={"dude"}
    )
    standalone_blackboard.dude = "Bob"

    root = create_root()

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(root, with_blackboard_variables=False)
        sys.exit()
    if args.render_with_blackboard_variables:
        py_trees.display.render_dot_tree(root, with_blackboard_variables=True)
        sys.exit()

    ####################
    # Execute
    ####################
    root.setup_with_descendants()
    blackboard = py_trees.blackboard.BlackboardClient(name="Unsetter", write={"foo"})
    print("\n--------- Tick 0 ---------\n")
    root.tick_once()
    print("\n")
    print(py_trees.display.unicode_tree(root, show_status=True))
    print("--------------------------\n")
    print(py_trees.display.unicode_blackboard())
    print("--------------------------\n")
    print(py_trees.display.unicode_blackboard(display_only_key_metadata=True))
    print("--------------------------\n")
    blackboard.unset("foo")
    print(py_trees.display.unicode_blackboard_activity_stream())

py-trees-demo-context-switching

Demonstrates context switching with parallels and sequences.

A context switching behaviour is run in parallel with a work sequence. Switching the context occurs in the initialise() and terminate() methods of the context switching behaviour. Note that whether the sequence results in failure or success, the context switch behaviour will always call the terminate() method to restore the context. It will also call terminate() to restore the context in the event of a higher priority parent cancelling this parallel subtree.

usage: py-trees-demo-context-switching [-h] [-r]

Named Arguments

-r, --render

render dot tree to file Default: False

class py_trees.demos.context_switching.ContextSwitch(name='ContextSwitch')

Bases: py_trees.behaviour.Behaviour

An example of a context switching class that sets (in initialise()) and restores a context (in terminate()). Use in parallel with a sequence/subtree that does the work while in this context.

Attention

Simply setting a pair of behaviours (set and reset context) on either end of a sequence will not suffice for context switching. In the case that one of the work behaviours in the sequence fails, the final reset context switch will never trigger.

__init__(name='ContextSwitch')

Initialize self. See help(type(self)) for accurate signature.

initialise()

Backup and set a new context.

terminate(new_status)

Restore the context with the previously backed up context.

update()

Just returns RUNNING while it waits for other activities to finish.

py_trees.demos.context_switching.main()

Entry point for the demo script.

py_trees/demos/contex_switching.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.context_switching
   :func: command_line_argument_parser
   :prog: py-trees-demo-context-switching

.. graphviz:: dot/demo-context_switching.dot

.. image:: images/context_switching.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Demonstrates context switching with parallels and sequences.\n"
    content += "\n"
    content += "A context switching behaviour is run in parallel with a work sequence.\n"
    content += "Switching the context occurs in the initialise() and terminate() methods\n"
    content += "of the context switching behaviour. Note that whether the sequence results\n"
    content += "in failure or success, the context switch behaviour will always call the\n"
    content += "terminate() method to restore the context. It will also call terminate()\n"
    content += "to restore the context in the event of a higher priority parent cancelling\n"
    content += "this parallel subtree.\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Context Switching".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    parser.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    return parser


class ContextSwitch(py_trees.behaviour.Behaviour):
    """
    An example of a context switching class that sets (in ``initialise()``)
    and restores a context (in ``terminate()``). Use in parallel with a
    sequence/subtree that does the work while in this context.

    .. attention:: Simply setting a pair of behaviours (set and reset context) on
        either end of a sequence will not suffice for context switching. In the case
        that one of the work behaviours in the sequence fails, the final reset context
        switch will never trigger.

    """
    def __init__(self, name="ContextSwitch"):
        super(ContextSwitch, self).__init__(name)
        self.feedback_message = "no context"

    def initialise(self):
        """
        Backup and set a new context.
        """
        self.logger.debug("%s.initialise()[switch context]" % (self.__class__.__name__))
        # Some actions that:
        #   1. retrieve the current context from somewhere
        #   2. cache the context internally
        #   3. apply a new context
        self.feedback_message = "new context"

    def update(self):
        """
        Just returns RUNNING while it waits for other activities to finish.
        """
        self.logger.debug("%s.update()[RUNNING][%s]" % (self.__class__.__name__, self.feedback_message))
        return py_trees.common.Status.RUNNING

    def terminate(self, new_status):
        """
        Restore the context with the previously backed up context.
        """
        self.logger.debug("%s.terminate()[%s->%s][restore context]" % (self.__class__.__name__, self.status, new_status))
        # Some actions that:
        #   1. restore the cached context
        self.feedback_message = "restored context"


def create_root():
    root = py_trees.composites.Parallel(name="Parallel", policy=py_trees.common.ParallelPolicy.SuccessOnOne())
    context_switch = ContextSwitch(name="Context")
    sequence = py_trees.composites.Sequence(name="Sequence")
    for job in ["Action 1", "Action 2"]:
        success_after_two = py_trees.behaviours.Count(name=job,
                                                      fail_until=0,
                                                      running_until=2,
                                                      success_until=10)
        sequence.add_child(success_after_two)
    root.add_child(context_switch)
    root.add_child(sequence)
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    print(description())
    py_trees.logging.level = py_trees.logging.Level.DEBUG

    root = create_root()

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(root)
        sys.exit()

    ####################
    # Execute
    ####################
    root.setup_with_descendants()
    for i in range(1, 6):
        try:
            print("\n--------- Tick {0} ---------\n".format(i))
            root.tick_once()
            print("\n")
            print("{}".format(py_trees.display.unicode_tree(root, show_status=True)))
            time.sleep(1.0)
        except KeyboardInterrupt:
            break
    print("\n")

py-trees-demo-dot-graphs

Renders a dot graph for a simple tree, with blackboxes.

usage: py-trees-demo-dot-graphs [-h]
                                [-l {all,fine_detail,detail,component,big_picture}]

Named Arguments

-l, --level

Possible choices: all, fine_detail, detail, component, big_picture visibility level Default: “fine_detail”

py_trees.demos.dot_graphs.main()

Entry point for the demo script.

py_trees/demos/dot_graphs.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.dot_graphs
   :func: command_line_argument_parser
   :prog: py-trees-demo-dot-graphs

.. graphviz:: dot/demo-dot-graphs.dot

"""

##############################################################################
# Imports
##############################################################################

import argparse
import subprocess
import py_trees

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    name = "py-trees-demo-dot-graphs"
    content = "Renders a dot graph for a simple tree, with blackboxes.\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Dot Graphs".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += console.white
        s += console.bold + "    Generate Full Dot Graph" + console.reset + "\n"
        s += "\n"
        s += console.cyan + "        {0}".format(name) + console.reset + "\n"
        s += "\n"
        s += console.bold + "    With Varying Visibility Levels" + console.reset + "\n"
        s += "\n"
        s += console.cyan + "        {0}".format(name) + console.yellow + " --level=all" + console.reset + "\n"
        s += console.cyan + "        {0}".format(name) + console.yellow + " --level=detail" + console.reset + "\n"
        s += console.cyan + "        {0}".format(name) + console.yellow + " --level=component" + console.reset + "\n"
        s += console.cyan + "        {0}".format(name) + console.yellow + " --level=big_picture" + console.reset + "\n"
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    parser.add_argument('-l', '--level', action='store',
                        default='fine_detail',
                        choices=['all', 'fine_detail', 'detail', 'component', 'big_picture'],
                        help='visibility level')
    return parser


def create_tree(level):
    root = py_trees.composites.Selector("Demo Dot Graphs %s" % level)
    first_blackbox = py_trees.composites.Sequence("BlackBox 1")
    first_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    first_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    first_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    first_blackbox.blackbox_level = py_trees.common.BlackBoxLevel.BIG_PICTURE
    second_blackbox = py_trees.composites.Sequence("Blackbox 2")
    second_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    second_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    second_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    second_blackbox.blackbox_level = py_trees.common.BlackBoxLevel.COMPONENT
    third_blackbox = py_trees.composites.Sequence("Blackbox 3")
    third_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    third_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    third_blackbox.add_child(py_trees.behaviours.Running("Worker"))
    third_blackbox.blackbox_level = py_trees.common.BlackBoxLevel.DETAIL
    root.add_child(first_blackbox)
    root.add_child(second_blackbox)
    first_blackbox.add_child(third_blackbox)
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    args.enum_level = py_trees.common.string_to_visibility_level(args.level)
    print(description())
    py_trees.logging.level = py_trees.logging.Level.DEBUG

    root = create_tree(args.level)
    py_trees.display.render_dot_tree(root, args.enum_level)

    if py_trees.utilities.which("xdot"):
        try:
            subprocess.call(["xdot", "demo_dot_graphs_%s.dot" % args.level])
        except KeyboardInterrupt:
            pass
    else:
        print("")
        console.logerror("No xdot viewer found, skipping display [hint: sudo apt install xdot]")
        print("")

py-trees-demo-logging

A demonstration of logging with trees.

This demo utilises a SnapshotVisitor to trigger a post-tick handler to dump a serialisation of the tree to a json log file.

This coupling of visitor and post-tick handler can be used for any kind of event handling - the visitor is the trigger and the post-tick handler the action. Aside from logging, the most common use case is to serialise the tree for messaging to a graphical, runtime monitor.

usage: py-trees-demo-logging [-h] [-r | -i]

Named Arguments

-r, --render	render dot tree to file Default: False
-i, --interactive
	pause and wait for keypress at each tick Default: False

py_trees.demos.logging.logger(snapshot_visitor, behaviour_tree)

A post-tick handler that logs the tree (relevant parts thereof) to a yaml file.

py_trees.demos.logging.main()

Entry point for the demo script.

py_trees/demos/logging.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.logging
   :func: command_line_argument_parser
   :prog: py-trees-demo-logging

.. graphviz:: dot/demo-logging.dot

.. image:: images/logging.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import functools
import json
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description(root):
    content = "A demonstration of logging with trees.\n\n"
    content += "This demo utilises a SnapshotVisitor to trigger\n"
    content += "a post-tick handler to dump a serialisation of the\n"
    content += "tree to a json log file.\n"
    content += "\n"
    content += "This coupling of visitor and post-tick handler can be\n"
    content += "used for any kind of event handling - the visitor is the\n"
    content += "trigger and the post-tick handler the action. Aside from\n"
    content += "logging, the most common use case is to serialise the tree\n"
    content += "for messaging to a graphical, runtime monitor.\n"
    content += "\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Logging".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(create_tree()),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    group = parser.add_mutually_exclusive_group()
    group.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    group.add_argument('-i', '--interactive', action='store_true', help='pause and wait for keypress at each tick')
    return parser


def logger(snapshot_visitor, behaviour_tree):
    """
    A post-tick handler that logs the tree (relevant parts thereof) to a yaml file.
    """
    if snapshot_visitor.changed:
        print(console.cyan + "Logging.......................yes\n" + console.reset)
        tree_serialisation = {
            'tick': behaviour_tree.count,
            'nodes': []
        }
        for node in behaviour_tree.root.iterate():
            node_type_str = "Behaviour"
            for behaviour_type in [py_trees.composites.Sequence,
                                   py_trees.composites.Selector,
                                   py_trees.composites.Parallel,
                                   py_trees.decorators.Decorator]:
                if isinstance(node, behaviour_type):
                    node_type_str = behaviour_type.__name__
            node_snapshot = {
                'name': node.name,
                'id': str(node.id),
                'parent_id': str(node.parent.id) if node.parent else "none",
                'child_ids': [str(child.id) for child in node.children],
                'tip_id': str(node.tip().id) if node.tip() else 'none',
                'class_name': str(node.__module__) + '.' + str(type(node).__name__),
                'type': node_type_str,
                'status': node.status.value,
                'message': node.feedback_message,
                'is_active': True if node.id in snapshot_visitor.visited else False
                }
            tree_serialisation['nodes'].append(node_snapshot)
        if behaviour_tree.count == 0:
            with open('dump.json', 'w+') as outfile:
                json.dump(tree_serialisation, outfile, indent=4)
        else:
            with open('dump.json', 'a') as outfile:
                json.dump(tree_serialisation, outfile, indent=4)
    else:
        print(console.yellow + "Logging.......................no\n" + console.reset)


def create_tree():
    every_n_success = py_trees.behaviours.SuccessEveryN("EveryN", 5)
    sequence = py_trees.composites.Sequence(name="Sequence")
    guard = py_trees.behaviours.Success("Guard")
    periodic_success = py_trees.behaviours.Periodic("Periodic", 3)
    finisher = py_trees.behaviours.Success("Finisher")
    sequence.add_child(guard)
    sequence.add_child(periodic_success)
    sequence.add_child(finisher)
    sequence.blackbox_level = py_trees.common.BlackBoxLevel.COMPONENT
    idle = py_trees.behaviours.Success("Idle")
    root = py_trees.composites.Selector(name="Logging")
    root.add_child(every_n_success)
    root.add_child(sequence)
    root.add_child(idle)
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    py_trees.logging.level = py_trees.logging.Level.DEBUG
    tree = create_tree()
    print(description(tree))

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(tree)
        sys.exit()

    ####################
    # Tree Stewardship
    ####################
    behaviour_tree = py_trees.trees.BehaviourTree(tree)

    debug_visitor = py_trees.visitors.DebugVisitor()
    snapshot_visitor = py_trees.visitors.DisplaySnapshotVisitor()

    behaviour_tree.visitors.append(debug_visitor)
    behaviour_tree.visitors.append(snapshot_visitor)

    behaviour_tree.add_post_tick_handler(functools.partial(logger, snapshot_visitor))

    behaviour_tree.setup(timeout=15)

    ####################
    # Tick Tock
    ####################
    if args.interactive:
        py_trees.console.read_single_keypress()
    while True:
        try:
            behaviour_tree.tick()
            if args.interactive:
                py_trees.console.read_single_keypress()
            else:
                time.sleep(0.5)
        except KeyboardInterrupt:
            break
    print("\n")

py-trees-demo-selector

Higher priority switching and interruption in the children of a selector.

In this example the higher priority child is setup to fail initially, falling back to the continually running second child. On the third tick, the first child succeeds and cancels the hitherto running child.

usage: py-trees-demo-selector [-h] [-r]

Named Arguments

-r, --render

render dot tree to file Default: False

py_trees.demos.selector.main()

Entry point for the demo script.

py_trees/demos/selector.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.selector
   :func: command_line_argument_parser
   :prog: py-trees-demo-selector

.. graphviz:: dot/demo-selector.dot

.. image:: images/selector.gif

"""
##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Higher priority switching and interruption in the children of a selector.\n"
    content += "\n"
    content += "In this example the higher priority child is setup to fail initially,\n"
    content += "falling back to the continually running second child. On the third\n"
    content += "tick, the first child succeeds and cancels the hitherto running child.\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Selectors".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    parser.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    return parser


def create_root():
    root = py_trees.composites.Selector("Selector")
    success_after_two = py_trees.behaviours.Count(name="After Two",
                                                  fail_until=2,
                                                  running_until=2,
                                                  success_until=10)
    always_running = py_trees.behaviours.Running(name="Running")
    root.add_children([success_after_two, always_running])
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    print(description())
    py_trees.logging.level = py_trees.logging.Level.DEBUG

    root = create_root()

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(root)
        sys.exit()

    ####################
    # Execute
    ####################
    root.setup_with_descendants()
    for i in range(1, 4):
        try:
            print("\n--------- Tick {0} ---------\n".format(i))
            root.tick_once()
            print("\n")
            print(py_trees.display.unicode_tree(root=root, show_status=True))
            time.sleep(1.0)
        except KeyboardInterrupt:
            break
    print("\n")

py-trees-demo-sequence

Demonstrates sequences in action.

A sequence is populated with 2-tick jobs that are allowed to run through to completion.

usage: py-trees-demo-sequence [-h] [-r]

Named Arguments

-r, --render

render dot tree to file Default: False

py_trees.demos.sequence.main()

Entry point for the demo script.

py_trees/demos/sequence.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.sequence
   :func: command_line_argument_parser
   :prog: py-trees-demo-sequence

.. graphviz:: dot/demo-sequence.dot

.. image:: images/sequence.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "Demonstrates sequences in action.\n\n"
    content += "A sequence is populated with 2-tick jobs that are allowed to run through to\n"
    content += "completion.\n"

    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Sequences".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    parser.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    return parser


def create_root():
    root = py_trees.composites.Sequence("Sequence")
    for action in ["Action 1", "Action 2", "Action 3"]:
        success_after_two = py_trees.behaviours.Count(name=action,
                                                      fail_until=0,
                                                      running_until=1,
                                                      success_until=10)
        root.add_child(success_after_two)
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    print(description())
    py_trees.logging.level = py_trees.logging.Level.DEBUG

    root = create_root()

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(root)
        sys.exit()

    ####################
    # Execute
    ####################
    root.setup_with_descendants()
    for i in range(1, 6):
        try:
            print("\n--------- Tick {0} ---------\n".format(i))
            root.tick_once()
            print("\n")
            print(py_trees.display.unicode_tree(root=root, show_status=True))
            time.sleep(1.0)
        except KeyboardInterrupt:
            break
    print("\n")

py-trees-demo-tree-stewardship

A demonstration of tree stewardship.

A slightly less trivial tree that uses a simple stdout pre-tick handler and both the debug and snapshot visitors for logging and displaying the state of the tree.

EVENTS

• 3 : sequence switches from running to success
• 4 : selector’s first child flicks to success once only
• 8 : the fallback idler kicks in as everything else fails
• 14 : the first child kicks in again, aborting a running sequence behind it

usage: py-trees-demo-tree-stewardship [-h]
                                      [-r | --render-with-blackboard-variables | -i]

Named Arguments

-r, --render	render dot tree to file Default: False
--render-with-blackboard-variables
	render dot tree to file with blackboard variables Default: False
-i, --interactive
	pause and wait for keypress at each tick Default: False

class py_trees.demos.stewardship.Finisher

Bases: py_trees.behaviour.Behaviour

__init__()

Initialize self. See help(type(self)) for accurate signature.

update()

Note

User Customisable Callback

Returns:the behaviour’s new status Status Return type:Status

Subclasses may override this method to perform any logic required to arrive at a decision on the behaviour’s new status. It is the primary worker function called on by the tick() mechanism.

Tip

This method should be almost instantaneous and non-blocking

class py_trees.demos.stewardship.PeriodicSuccess

Bases: py_trees.behaviours.Periodic

__init__()

Initialize self. See help(type(self)) for accurate signature.

update()

Note

User Customisable Callback

Returns:the behaviour’s new status Status Return type:Status

Subclasses may override this method to perform any logic required to arrive at a decision on the behaviour’s new status. It is the primary worker function called on by the tick() mechanism.

Tip

This method should be almost instantaneous and non-blocking

class py_trees.demos.stewardship.SuccessEveryN

Bases: py_trees.behaviours.SuccessEveryN

__init__()

Initialize self. See help(type(self)) for accurate signature.

update()

Note

User Customisable Callback

Returns:the behaviour’s new status Status Return type:Status

Subclasses may override this method to perform any logic required to arrive at a decision on the behaviour’s new status. It is the primary worker function called on by the tick() mechanism.

Tip

This method should be almost instantaneous and non-blocking

py_trees.demos.stewardship.main()

Entry point for the demo script.

py_trees/demos/stewardship.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.stewardship
   :func: command_line_argument_parser
   :prog: py-trees-demo-tree-stewardship

.. graphviz:: dot/demo-tree-stewardship.dot

.. image:: images/tree_stewardship.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description():
    content = "A demonstration of tree stewardship.\n\n"
    content += "A slightly less trivial tree that uses a simple stdout pre-tick handler\n"
    content += "and both the debug and snapshot visitors for logging and displaying\n"
    content += "the state of the tree.\n"
    content += "\n"
    content += "EVENTS\n"
    content += "\n"
    content += " -  3 : sequence switches from running to success\n"
    content += " -  4 : selector's first child flicks to success once only\n"
    content += " -  8 : the fallback idler kicks in as everything else fails\n"
    content += " - 14 : the first child kicks in again, aborting a running sequence behind it\n"
    content += "\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Trees".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    group = parser.add_mutually_exclusive_group()
    group.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    group.add_argument(
        '--render-with-blackboard-variables',
        action='store_true',
        help='render dot tree to file with blackboard variables'
    )
    group.add_argument('-i', '--interactive', action='store_true', help='pause and wait for keypress at each tick')
    return parser


def pre_tick_handler(behaviour_tree):
    print("\n--------- Run %s ---------\n" % behaviour_tree.count)


class SuccessEveryN(py_trees.behaviours.SuccessEveryN):
    def __init__(self):
        super().__init__(name="EveryN", n=5)
        self.blackboard.register_key("count", write=True)

    def update(self):
        status = super().update()
        self.blackboard.count = self.count
        return status


class PeriodicSuccess(py_trees.behaviours.Periodic):
    def __init__(self):
        super().__init__(name="Periodic", n=3)
        self.blackboard.register_key("period", write=True)

    def update(self):
        status = super().update()
        self.blackboard.period = self.period
        return status


class Finisher(py_trees.behaviour.Behaviour):
    def __init__(self):
        super().__init__(name="Finisher")
        self.blackboard.register_key("count", read=True)
        self.blackboard.register_key("period", read=True)

    def update(self):
        print(console.green + "---------------------------" + console.reset)
        print(console.bold + "        Finisher" + console.reset)
        print(console.green + "  Count : {}".format(self.blackboard.count) + console.reset)
        print(console.green + "  Period: {}".format(self.blackboard.period) + console.reset)
        print(console.green + "---------------------------" + console.reset)
        return py_trees.common.Status.SUCCESS


def create_tree():
    every_n_success = SuccessEveryN()
    sequence = py_trees.composites.Sequence(name="Sequence")
    guard = py_trees.behaviours.Success("Guard")
    periodic_success = PeriodicSuccess()
    finisher = Finisher()
    sequence.add_child(guard)
    sequence.add_child(periodic_success)
    sequence.add_child(finisher)
    idle = py_trees.behaviours.Success("Idle")
    root = py_trees.composites.Selector(name="Demo Tree")
    root.add_child(every_n_success)
    root.add_child(sequence)
    root.add_child(idle)
    return root


##############################################################################
# Main
##############################################################################

def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    py_trees.logging.level = py_trees.logging.Level.DEBUG
    tree = create_tree()
    print(description())

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(tree)
        sys.exit()

    if args.render_with_blackboard_variables:
        py_trees.display.render_dot_tree(tree, with_blackboard_variables=True)
        sys.exit()

    ####################
    # Tree Stewardship
    ####################
    py_trees.blackboard.Blackboard.enable_activity_stream(100)
    behaviour_tree = py_trees.trees.BehaviourTree(tree)
    behaviour_tree.add_pre_tick_handler(pre_tick_handler)
    behaviour_tree.visitors.append(py_trees.visitors.DebugVisitor())
    behaviour_tree.visitors.append(
        py_trees.visitors.DisplaySnapshotVisitor(
            display_blackboard=True,
            display_activity_stream=True)
    )
    behaviour_tree.setup(timeout=15)

    ####################
    # Tick Tock
    ####################
    if args.interactive:
        py_trees.console.read_single_keypress()
    while True:
        try:
            behaviour_tree.tick()
            if args.interactive:
                py_trees.console.read_single_keypress()
            else:
                time.sleep(0.5)
        except KeyboardInterrupt:
            break
    print("\n")

py-trees-demo-pick-up-where-you-left-off

A demonstration of the ‘pick up where you left off’ idiom.

A common behaviour tree pattern that allows you to resume work after being interrupted by a high priority interrupt.

EVENTS

• 2 : task one done, task two running
• 3 : high priority interrupt
• 7 : task two restarts
• 9 : task two done

usage: py-trees-demo-pick-up-where-you-left-off [-h] [-r | -i]

Named Arguments

-r, --render	render dot tree to file Default: False
-i, --interactive
	pause and wait for keypress at each tick Default: False

py_trees.demos.pick_up_where_you_left_off.main()

Entry point for the demo script.

py_trees.demos.pick_up_where_you_left_off.post_tick_handler(snapshot_visitor, behaviour_tree)

Prints an ascii tree with the current snapshot status.

py_trees.demos.pick_up_where_you_left_off.pre_tick_handler(behaviour_tree)

This prints a banner and will run immediately before every tick of the tree.

Parameters:behaviour_tree (BehaviourTree) – the tree custodian

py_trees/demos/pick_up_where_you_left_off.py

#!/usr/bin/env python
#
# License: BSD
#   https://raw.githubusercontent.com/splintered-reality/py_trees/devel/LICENSE
#
##############################################################################
# Documentation
##############################################################################

"""
.. argparse::
   :module: py_trees.demos.pick_up_where_you_left_off
   :func: command_line_argument_parser
   :prog: py-trees-demo-pick-up-where-you-left-off

.. graphviz:: dot/pick_up_where_you_left_off.dot

.. image:: images/pick_up_where_you_left_off.gif
"""

##############################################################################
# Imports
##############################################################################

import argparse
import functools
import py_trees
import sys
import time

import py_trees.console as console

##############################################################################
# Classes
##############################################################################


def description(root):
    content = "A demonstration of the 'pick up where you left off' idiom.\n\n"
    content += "A common behaviour tree pattern that allows you to resume\n"
    content += "work after being interrupted by a high priority interrupt.\n"
    content += "\n"
    content += "EVENTS\n"
    content += "\n"
    content += " -  2 : task one done, task two running\n"
    content += " -  3 : high priority interrupt\n"
    content += " -  7 : task two restarts\n"
    content += " -  9 : task two done\n"
    content += "\n"
    if py_trees.console.has_colours:
        banner_line = console.green + "*" * 79 + "\n" + console.reset
        s = "\n"
        s += banner_line
        s += console.bold_white + "Trees".center(79) + "\n" + console.reset
        s += banner_line
        s += "\n"
        s += content
        s += "\n"
        s += banner_line
    else:
        s = content
    return s


def epilog():
    if py_trees.console.has_colours:
        return console.cyan + "And his noodly appendage reached forth to tickle the blessed...\n" + console.reset
    else:
        return None


def command_line_argument_parser():
    parser = argparse.ArgumentParser(description=description(create_root()),
                                     epilog=epilog(),
                                     formatter_class=argparse.RawDescriptionHelpFormatter,
                                     )
    group = parser.add_mutually_exclusive_group()
    group.add_argument('-r', '--render', action='store_true', help='render dot tree to file')
    group.add_argument('-i', '--interactive', action='store_true', help='pause and wait for keypress at each tick')
    return parser


def pre_tick_handler(behaviour_tree):
    """
    This prints a banner and will run immediately before every tick of the tree.

    Args:
        behaviour_tree (:class:`~py_trees.trees.BehaviourTree`): the tree custodian

    """
    print("\n--------- Run %s ---------\n" % behaviour_tree.count)


def post_tick_handler(snapshot_visitor, behaviour_tree):
    """
    Prints an ascii tree with the current snapshot status.
    """
    print(
        "\n" + py_trees.display.unicode_tree(
            root=behaviour_tree.root,
            visited=snapshot_visitor.visited,
            previously_visited=snapshot_visitor.previously_visited
        )
    )


def create_root():
    task_one = py_trees.behaviours.Count(
        name="Task 1",
        fail_until=0,
        running_until=2,
        success_until=10
    )
    task_two = py_trees.behaviours.Count(
        name="Task 2",
        fail_until=0,
        running_until=2,
        success_until=10
    )
    high_priority_interrupt = py_trees.decorators.RunningIsFailure(
        child=py_trees.behaviours.Periodic(
            name="High Priority",
            n=3
        )
    )
    piwylo = py_trees.idioms.pick_up_where_you_left_off(
        name="Pick Up\nWhere You\nLeft Off",
        tasks=[task_one, task_two]
    )
    root = py_trees.composites.Selector(name="Root")
    root.add_children([high_priority_interrupt, piwylo])

    return root

##############################################################################
# Main
##############################################################################


def main():
    """
    Entry point for the demo script.
    """
    args = command_line_argument_parser().parse_args()
    py_trees.logging.level = py_trees.logging.Level.DEBUG
    root = create_root()
    print(description(root))

    ####################
    # Rendering
    ####################
    if args.render:
        py_trees.display.render_dot_tree(root)
        sys.exit()

    ####################
    # Tree Stewardship
    ####################
    behaviour_tree = py_trees.trees.BehaviourTree(root)
    behaviour_tree.add_pre_tick_handler(pre_tick_handler)
    behaviour_tree.visitors.append(py_trees.visitors.DebugVisitor())
    snapshot_visitor = py_trees.visitors.SnapshotVisitor()
    behaviour_tree.add_post_tick_handler(functools.partial(post_tick_handler, snapshot_visitor))
    behaviour_tree.visitors.append(snapshot_visitor)
    behaviour_tree.setup(timeout=15)

    ####################
    # Tick Tock
    ####################
    if args.interactive:
        py_trees.console.read_single_keypress()
    for unused_i in range(1, 11):
        try:
            behaviour_tree.tick()
            if args.interactive:
                py_trees.console.read_single_keypress()
            else:
                time.sleep(0.5)
        except KeyboardInterrupt:
            break
    print("\n")