02: Bug Tracker

Source: examples/02_bug_tracker.py

This example models an issue lifecycle (OPEN -> ASSIGNED -> DEFERRED/CLOSED) using external state storage on a domain object.

Run

uv run python examples/02_bug_tracker.py

What This Example Covers

• External state storage via state_accessor and state_mutator
• Trigger payloads with set_trigger_parameters(...)
• Entry actions bound to specific triggers with on_entry_from(...)
• Reentry transitions with permit_reentry(...)
• Hierarchy with substate_of(...)
• Capability checks and invalid-transition handling

Key APIs Used

sm = StateMachine(
    initial_state,
    state_accessor=lambda: self._state,
    state_mutator=lambda s: self._set_state(s),
)

sm.configure(State.ASSIGNED).on_entry_from(Trigger.ASSIGN, self._assign)
sm.set_trigger_parameters(Trigger.ASSIGN, str)

Notes

• The Bug class owns workflow behavior, while the machine drives allowed transitions.
• The example also prints reflection data and generates a graph image.