Guards

Guards control whether a configured behavior is valid for a fired trigger.

Where Guards Apply

• permit(...)
• permit_if(...)
• permit_reentry(...)
• permit_reentry_if(...)
• ignore(...)
• ignore_if(...)
• internal_transition(...)
• dynamic(...)

Guard Types

• Sync: def guard(...) -> bool
• Async: async def guard(...) -> bool

Sync and Async Rules

• fire(...) only supports sync guards.
• fire_async(...) supports sync and async guards.
• can_fire(...) and get_permitted_triggers(...) skip/raise when async guards are involved.
• can_fire_async(...) and get_permitted_triggers_async(...) evaluate async guards.

Guard Arguments

Guard functions can inspect trigger arguments. Guards receive a compatible prefix of the fired args.

def guard(order_total: float) -> bool:
    return order_total >= 100.0

sm.configure(State.A).permit_if(Trigger.X, State.B, guard)
sm.fire(Trigger.X, 120.0)

Guard Failure Behavior

When a trigger is valid but guard conditions fail, InvalidTransitionError is raised and includes unmet guard descriptions when provided.