python类继承，attributeError

Python class inheritance, attributeError

我用python编写了一个StateMachine类，这样它就可以从中继承。它的逻辑按预期工作，但我可以从名为StateMachineTest的派生StateMachine类中存在的State访问属性self.data。

生成以下错误：

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Traceback (most recent call last):
File"/home/nbout/work/python/state_machine/main.py", line 68, in
main()
File"/home/nbout/work/python/state_machine/main.py", line 59, in main
test = StateMachineTest()
File"/home/nbout/work/python/state_machine/main.py", line 47, in __init__
StateMachine.__init__(self, Started())
File"/home/nbout/work/python/state_machine/state_machine.py", line 17, in _init__
self.current_state.on_enter(self)
File"/home/nbout/work/python/state_machine/main.py", line 16, in on_enter
print("Started: data:{}".format(sm_test.data))
Started: on_enter
AttributeError: 'StateMachineTest' object has no attribute 'data'
Started: on_exit

状态机.py

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class State:

def on_enter(self, state_machine):
pass

def on_exit(self, state_machine):
pass

class StateMachine:

def __init__(self, start_state):
self.current_state = start_state

self.current_state.on_enter(self)

def __del__(self):
self.current_state.on_exit(self)

def set_state(self, state):

self.current_state.on_exit(self)
self.current_state = state
self.current_state.on_enter(self)

Me.Py

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from state_machine import StateMachine
from state_machine import State

class StateTest(State):
def pause(self, state_machine_test):
pass

def start(self, state_machine_test):
pass

class Started(StateTest):
def on_enter(self, sm_test):
print("Started: on_enter")
print("Started: data:{}".format(sm_test.data))

def on_exit(self, sm_test):
print("Started: on_exit")

def pause(self, sm_test):
print("Started: pause")
sm_test.set_state(Paused())

def start(self, sm_test):
print("Started: start")

class Paused(StateTest):
def on_enter(self, sm_test):
print("Paused: on_enter")

def on_exit(self, sm_test):
print("Paused: on_exit")

def pause(self, sm_test):
print("Paused: pause")

def start(self, sm_test):
print("Paused: start")
sm_test.set_state(Started())

class StateMachineTest(StateMachine):

def __init__(self):
StateMachine.__init__(self, Started())
self.data = 10

def pause(self):
self.current_state.pause(self)

def start(self):
self.current_state.start(self)

def main():

test = StateMachineTest()

test.start()
test.pause()
test.pause()
test.start()

if __name__ == '__main__':
main()

你的问题在于，StateMachine.__init__(self, Started())要求self的data属性已经设置，但你只设置下一行(self.data = 10)。切换这两条线，然后再试一次！