问题描述
作为与 this answer 无关的后续，它使用以下工作代码：
from transitions import Machine
from transitions import EventData
from typing import Callable
from enum import Enum,auto
class Observer:
def state_changed(self,event_data: EventData):
print(f"state is Now '{event_data.state.name}'")
class State(Enum):
SOLID = auto()
LIQUID = auto()
GAS = auto()
class SubscribableMachine(Machine):
transitions = [
{'trigger': 'heat','source': State.soLID,'dest': State.LIQUID},{'trigger': 'heat','source': State.LIQUID,'dest': State.GAS},{'trigger': 'cool','source': State.GAS,'dest': State.soLID}
]
def __init__(self):
super().__init__(states=State,transitions=self.transitions,initial=State.soLID,send_event=True)
def subscribe(self,func: Callable,state: State):
self.get_state(state).on_enter.append(func)
def unsubscribe(self,state: State):
self.get_state(state).on_enter.remove(func)
machine = SubscribableMachine()
observer = Observer()
machine.subscribe(observer.state_changed,State.LIQUID)
machine.heat() # >>> state is Now 'LIQUID'
machine.heat()
assert machine.state == State.GAS
machine.unsubscribe(observer.state_changed,State.LIQUID)
machine.cool() # no output
assert machine.state == State.LIQUID
我也想要 Trigger 的枚举，就像 State 的枚举一样。
唉，当我尝试时
class Trigger(Enum):
heat = auto()
cool = auto()
和
transitions = [
{'trigger': Trigger.heat,{'trigger': Trigger.heat,{'trigger': Trigger.cool,'dest': State.soLID}
]
def __init__(self):
super().__init__(states=State,send_event=True)
我明白
Traceback (most recent call last):
File "C:/code/EPMD/Kodex/Algorithms/src/python/epmd/ablation_points/queries/dfgfdsg.py",line 42,in <module>
machine = SubscribableMachine()
File "C:/code/EPMD/Kodex/Algorithms/src/python/epmd/ablation_points/queries/dfgfdsg.py",line 33,in __init__
initial=State.soLID,send_event=True)
File "C:\Code\EPMD\Kodex\EPD_Prerequisite\python_3.7.6\Lib\site-packages\transitions\core.py",line 589,in __init__
self.add_model(model)
File "C:\Code\EPMD\Kodex\EPD_Prerequisite\python_3.7.6\Lib\site-packages\transitions\core.py",line 607,in add_model
self._add_trigger_to_model(trigger,mod)
File "C:\Code\EPMD\Kodex\EPD_Prerequisite\python_3.7.6\Lib\site-packages\transitions\core.py",line 813,in _add_trigger_to_model
self._checked_assignment(model,trigger,partial(self.events[trigger].trigger,model))
File "C:\Code\EPMD\Kodex\EPD_Prerequisite\python_3.7.6\Lib\site-packages\transitions\core.py",line 807,in _checked_assignment
if hasattr(model,name):
TypeError: hasattr(): attribute name must be string
我可以使用Enum的{{1}}来解决它：
.name但是 transitions = [
{'trigger': Trigger.heat.name,{'trigger': Trigger.heat.name,{'trigger': Trigger.cool.name,'dest': State.soLID}
]
和 State 之间的不对称让我很困扰。
难道我做错了什么？为什么枚举适用于 Trigger 而不适用于 State？
解决方法
错误说明正确：
TypeError: hasattr(): attribute name must be string。如果您阅读枚举文档 (https://docs.python.org/3/library/enum.html)，您将看到每个函数返回的内容。您可以覆盖它们，看看是否有效。除非 Machine 中的代码专门检查 Enum 并将其转换为字符串，否则它不会工作。
使其工作的更简单方法，以您希望的方式执行以下操作：
class Trigger:
HEAT = 'HEAT'
COOL = 'COOL'
正如 vish 已经指出的，没有办法直接使用枚举作为触发器。 Transitions 将触发器名称作为方法绑定到模型，因此要求触发器是字符串。但是，Machine 和所有子类在编写时都考虑到了继承。如果你想使用枚举而不是类和类属性，你可以派生一个合适的EnumTransitionMachine并得到一个统一的接口：
from transitions import Machine
from enum import Enum,auto
class State(Enum):
A = auto()
B = auto()
C = auto()
class Transitions(Enum):
GO = auto()
PROCEED = auto()
class EnumTransitionMachine(Machine):
def add_transition(self,trigger,*args,**kwargs):
super().add_transition(trigger.name.lower() if hasattr(trigger,'name') else trigger,**kwargs)
transitions = [[Transitions.GO,State.A,State.B],[Transitions.PROCEED,State.B,State.C]]
m = EnumTransitionMachine(states=State,transitions=transitions,initial=State.A)
m.go()
assert m.state == State.B
m.proceed()
assert m.is_C()
仅供参考：还可以将 Enums 与字符串值一起使用：
class State(Enum):
A = "A"
B = "B"
C = "C"
class Transitions(Enum):
GO = "GO"
PROCEED = "PROCEED"
# you could use the enum's value then instead:
def add_transition(self,**kwargs):
super().add_transition(trigger.value.lower() if hasattr(trigger,'value') else trigger,**kwargs)