State Machine

A state machine is a model used to describe the transitions of an object between different states. It clearly shows how an object changes state based on events and may trigger corresponding actions.

Core Concepts

• State: A distinct mode or condition of the system (e.g. “Idle”, “Running”). Managed by State class with optional on_enter/on_exit callbacks

• Event: A trigger signal that may cause state transitions (e.g. “start”, “stop”)

• Transition: A state change path from source to destination state triggered by an event

• Action: An operation executed during transition (before entering new state)

• Guard: A precondition that must be satisfied to allow transition

Code Link

class MissionPlanning.StateMachine.state_machine.StateMachine(name: str, model=<class 'object'>)

__init__(name: str, model=<class 'object'>)

Initialize the state machine.

Parameters:

• name (str) – Name of the state machine.

• model (object, optional) – Model object used to automatically look up callback functions for states and transitions: State callbacks: Automatically searches for ‘on_enter_<state>’ and ‘on_exit_<state>’ methods. Transition callbacks: When action or guard parameters are strings, looks up corresponding methods in the model.

Example

>>> class MyModel:
...     def on_enter_idle(self):
...         print("Entering idle state")
...     def on_exit_idle(self):
...         print("Exiting idle state")
...     def can_start(self):
...         return True
...     def on_start(self):
...         print("Starting operation")
>>> model = MyModel()
>>> machine = StateMachine("my_machine", model)

add_transition(src_state: str | State, event: str, dst_state: str | State, guard: str | Callable = None, action: str | Callable = None) → None

Add a transition to the state machine.

Parameters:

• src_state (str | State) – The source state where the transition begins. Can be either a state name or a State object.

• event (str) – The event that triggers this transition.

• dst_state (str | State) – The destination state where the transition ends. Can be either a state name or a State object.

• guard (str | Callable, optional) – Guard condition for the transition. If callable: Function that returns bool. If str: Name of a method in the model class. If returns True: Transition proceeds. If returns False: Transition is skipped.

• action (str | Callable, optional) – Action to execute during transition. If callable: Function to execute. If str: Name of a method in the model class. Executed after guard passes and before entering new state.

Example

>>> machine.add_transition(
...     src_state="idle",
...     event="start",
...     dst_state="running",
...     guard="can_start",
...     action="on_start"
... )

process(event: str) → None

Process an event in the state machine.

Parameters:

event – Event name.

Example

>>> machine.process("start")

register_state(state: str | State, on_enter=None, on_exit=None)

Register a state in the state machine.

Parameters:

• state (str | State) – The state to register. Can be either a string (state name) or a State object.

• on_enter (Callable, optional) – Callback function to be executed when entering the state. If state is a string and on_enter is None, it will look for a method named ‘on_enter_<state>’ in the model.

• on_exit (Callable, optional) – Callback function to be executed when exiting the state. If state is a string and on_exit is None, it will look for a method named ‘on_exit_<state>’ in the model.

Example

>>> machine.register_state("idle", on_enter=on_enter_idle, on_exit=on_exit_idle)
>>> machine.register_state(State("running", on_enter=on_enter_running, on_exit=on_exit_running))

PlantUML Support

The generate_plantuml() method creates diagrams showing:

• Current state (marked with [*] arrow)

• All possible transitions

• Guard conditions in [brackets]

• Actions prefixed with /

Example

state machine diagram:

state transition table:

State Transitions

Source State	Event	Target State	Guard	Action
patrolling	detect_task	executing_task
executing_task	task_complete	patrolling		reset_task
executing_task	low_battery	returning_to_base	is_battery_low
returning_to_base	reach_base	charging
charging	charge_complete	patrolling