aleneum
commented
3 years ago Hello @S1MP50N,
transitions differentiates between a Machine which defines transitions, events and state objects and a Model which is the actual stateful object and defines all callbacks that should be resolved by name. When you do not explicitely pass a model to a machine, the machine itself will act as a model.
The documentation states that
However, since 0.8.0 (Nested)State instances are just referenced which means changes in one machine's collection of states and events will influence the other machine instance. Models and their state will not be shared though.
When you instantiate your parent machine and pass an already instantiated child machine, it will only reference state objects and transitions from the child machine. But it will be the parent that acts as a model. There have been several issues discussing this (e.g. #457, #456). You could either split your machine and model definitions or pass callbacks by reference instead of by name (self.top_bottom_transition instead of 'top_bottom_transition')
from transitions.extensions import HierarchicalMachine
class ChildFSM(HierarchicalMachine):
def top_bottom_transition(self):
print("top -> bottom")
def bottom_top_transition(self):
print("bottom -> top")
def __init__(self):
states = ['top', 'bottom']
HierarchicalMachine.__init__(self, states=states, initial='top', auto_transitions=False)
self.add_transition('down', 'top', 'bottom', after=self.top_bottom_transition)
self.add_transition('up', 'bottom', 'top', after=self.bottom_top_transition)
class ParentFSM(HierarchicalMachine):
def init_running_transition(self):
print("init->running")
def __init__(self, running):
states = ['init', {'name': 'running', 'children': running}]
HierarchicalMachine.__init__(self, states=states, initial='init', auto_transitions=False)
self.add_transition('start', 'init', 'running', after=self.init_running_transition)
childFSM = ChildFSM()
parentFSM = ParentFSM(childFSM)
print(parentFSM.state)
parentFSM.start()
print(parentFSM.state)
parentFSM.down()
print(parentFSM.state)
parentFSM.up()
print(parentFSM.state)However, childFSM's state will be independent of the state of parentFSM.
S1MP50N
Hi,
I am attempting to create a set of nested hierarchical state machines. As part of the application logic handling, I want to use the "after" callback on specific transitions to perform code actions. In order to keep the functionality co-located with each discrete machine the after callback methods are defined within each Machine class. This results in an exception that the 'after' method cannot be found when invoking events on the parent fsm? This feels incorrect? It would make sense that it should reference the child Machine class for the method (either if not found in the parent or as an override of the parents method possibly).
I have created a simplified code example which demonstrates the exception.
Error
Any assistance would be appreciated.
Thanks, Shaun