PyBT

A lightweight behavior tree implementation in python.

How to use it

Clone this repo and make sure the pybt package folder is in your PYTHONPATH environment variable. Try with import pybt to make sure it can be found.

• BehaviorTree class - is the implementation of the actual behavior tree. Here the nodes are traversed and the actions/conditions called.
• Actor class - A class that should be extended to run the actions and conditions of the behavior tree.
• Status class - More of an enum really (Status.SUCCESS, Status.RUNNING, Status.FAIL). Have to be returned by every action/condition in the actor class.
• BehaviorTree tick - The behavior tree has to be 'ticked' to call actions/conditions. This may be done for example once every update loop.

Writing behavior trees

Behavior trees can be supplied by passing a string or a filename when creating the BehaviorTree class.

Actions/conditions

Actions and conditions should be written on its own line. Underscores in action/condition-names are allowed.

my_first_action
my_second_action

Sequence

The sequence selector starts with a > and ends with <. Every action/conditon or other node inside the sequence selector runs one after another, from the top, until one returns Status.FAIL.

>
  my_first_action
  my_second_action
<

Priority

The priority selector starts with a ? and ends with !. Every action/condition or other node inside the priority selector runs one after another, from the top, until one returns Status.SUCCESS

?
  my_first_action
  my_second_action
!

Parallel

The parallel selector starts with a // or /n/ and ends with \\. The number n decides how many actions/conditions/nodes inside the parallel selector that atleast must return success for the parallel node to return success. If n is not provided every action/condition or other node must succeed for the parallel node to succeed. Every action/condition or other node inside the parallel selector is ticked once and then the response is examined.

//
  my_first_action
  my_second_action
\\

Comments

Lines starting with # will be ignored.

# This is a comment
action # You can comment on the same line as well

Importing subtrees/files

Importing other trees from files is also supported. File imports should be done on a new line and with the file path starting with :

:my_behavior_trees/behavior_tree.bt

Example

This simple example first defines an actor class MyActor with some actions and conditions. Then a behavior tree is created. The root node in the tree is a priority node, which will stop only when an action/condition/node has succeeded. It first checks if too much time as passed, which in the first 3 seconds has not and therefore returns Status.FAIL. The priority node tries the sequence node. The sequence node will return success if all actions/conditions/nodes in it returns success. This will not happen until enough_time_has_passed returns true - after 1.5 seconds. After this time the condition returns true and my_action is called printing "My Action was called!" until too_much_time_has_passed starts returning success - after another 1.5 seconds.

from pybt.behavior_tree import BehaviorTree, Status
from pybt.actor import Actor

from time import time, sleep

class MyActor(Actor):
  """My actor implementation. Runs the actions/conditions from my behavior tree!"""
  def __init__(self):
    Actor.__init__(self)
    self.time = time()

  def my_action(self, state):
    print "My Action was called!"
    return Status.SUCCESS

  def enough_time_has_passed(self, state):
    if (time()-self.time) > 1.5:
      return Status.SUCCESS
    return Status.FAIL

  def too_much_time_has_passed(self, state):
    if (time()-self.time) > 3:
      return Status.SUCCESS
    return Status.FAIL

if __name__=="__main__":
  # Behavior tree may also be supplied as a file
  # bt = BehaviorTree(MyActor(), "my_behavior_tree.bt")
  bt = BehaviorTree(MyActor(), behavior_tree="""
    ?
      too_much_time_has_passed
      >
        enough_time_has_passed
        my_action
      <
    !
    """)
  while True:
    print "Tick tock"
    bt.tick() # You may supply a state object in the tick method that
              # is passwed to all actions as a parameter. Default: None
    sleep(0.5)

Running the tests

Easiest way to run all tests is with nose.

nosetests pybt

You can also run individual test suits.

python -m pybt.tests.test_parser

Can also be nice to run specific test cases

python -m pybt.tests.test_parser TestParser.test_nested_prio

Contributing

Write some code with test and make a pull request! Any additions are welcome!

TODO

• Graphical representation of the tree
• Behavior tree runner (no need to provide custom loop)