A state machine is most useful when it can tell you what is possible right now, to enable the right buttons, or know when an order is finished. All three answers come straight from the transition table for the current state.
can(event): is event allowed from the current state?available_events(): the list of events allowed right nowis_terminal(): true when the current state has no outgoing eventsclass Order:
TRANSITIONS = {
"cart": {"checkout": "pending"},
"pending": {"pay": "paid", "cancel": "cancelled"},
"paid": {"ship": "shipped", "refund": "cancelled"},
"shipped": {"deliver": "delivered"},
"delivered": {},
"cancelled": {},
}
def __init__(self):
self.state = "cart"
def fire(self, event):
allowed = self.TRANSITIONS.get(self.state, {})
if event in allowed:
self.state = allowed[event]
return True
return False
def can(self, event):
"""Is this event allowed from the current state?"""
# TODO: return event in self.TRANSITIONS.get(self.state, {})
pass
def available_events(self):
"""List the events allowed from the current state."""
# TODO: return list(self.TRANSITIONS.get(self.state, {}).keys())
pass
def is_terminal(self):
"""True when no events are possible from the current state."""
# TODO: return len(self.TRANSITIONS.get(self.state, {})) == 0
pass
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A state machine is most useful when it can tell you what is possible right now, to enable the right buttons, or know when an order is finished. All three answers come straight from the transition table for the current state.
can(event): is event allowed from the current state?available_events(): the list of events allowed right nowis_terminal(): true when the current state has no outgoing eventsPress Run Tests or ⌘↩ to check your solution.