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Nesting State Machines

Description: This tutorial gives an example of nesting a state machine in another state machine, creating a hierarchical state machine.

Tutorial Level: BEGINNER

Next Tutorial: Concurrent States

All of the following examples can be run without modification. They can be found in the smach_tutorials package in the examples directory. The comments at the head of each file show roughly what the output from running the script should look like.

state_machine_nested2.png

https://raw.githubusercontent.com/eacousineau/executive_smach_tutorials/hydro-devel/smach_tutorials/examples/state_machine_nesting2.py

   1 #!/usr/bin/env python
   2 
   3 import roslib; roslib.load_manifest('smach_tutorials')
   4 import rospy
   5 import smach
   6 import smach_ros
   7 
   8 # define state Foo
   9 class Foo(smach.State):
  10     def __init__(self):
  11         smach.State.__init__(self, outcomes=['outcome1','outcome2'])
  12         self.counter = 0
  13 
  14     def execute(self, userdata):
  15         rospy.loginfo('Executing state FOO')
  16         if self.counter < 3:
  17             self.counter += 1
  18             return 'outcome1'
  19         else:
  20             return 'outcome2'
  21 
  22 
  23 # define state Bar
  24 class Bar(smach.State):
  25     def __init__(self):
  26         smach.State.__init__(self, outcomes=['outcome1'])
  27 
  28     def execute(self, userdata):
  29         rospy.loginfo('Executing state BAR')
  30         return 'outcome1'
  31         
  32 
  33 
  34 # define state Bas
  35 class Bas(smach.State):
  36     def __init__(self):
  37         smach.State.__init__(self, outcomes=['outcome3'])
  38 
  39     def execute(self, userdata):
  40         rospy.loginfo('Executing state BAS')
  41         return 'outcome3'
  42 
  43 
  44 
  45 
  46 def main():
  47     rospy.init_node('smach_example_state_machine')
  48 
  49     # Create the top level SMACH state machine
  50     sm_top = smach.StateMachine(outcomes=['outcome5'])
  51     
  52     # Open the container
  53     with sm_top:
  54 
  55         smach.StateMachine.add('BAS', Bas(),
  56                                transitions={'outcome3':'SUB'})
  57 
  58         # Create the sub SMACH state machine
  59         sm_sub = smach.StateMachine(outcomes=['outcome4'])
  60 
  61         # Open the container
  62         with sm_sub:
  63 
  64             # Add states to the container
  65             smach.StateMachine.add('FOO', Foo(), 
  66                                    transitions={'outcome1':'BAR', 
  67                                                 'outcome2':'outcome4'})
  68             smach.StateMachine.add('BAR', Bar(), 
  69                                    transitions={'outcome1':'FOO'})
  70 
  71         smach.StateMachine.add('SUB', sm_sub,
  72                                transitions={'outcome4':'outcome5'})
  73 
  74     # Execute SMACH plan
  75     outcome = sm_top.execute()
  76 
  77 
  78 
  79 if __name__ == '__main__':
  80     main()

Wiki: smach/Tutorials/Nesting State Machines (last edited 2016-01-21 10:02:56 by JavierVGomez)