使用转换库在 python 中的 FSM 中状态不会改变答案

【问题标题】：state do not change in a FSM in python using transitions library使用转换库在 python 中的 FSM 中状态不会改变
【发布时间】：2020-09-27 20:31:38
【问题描述】：

我正在尝试从 talk 复制代码：

class Video:
    ## Define the states
    PLAYING = "playing"
    PAUSED = "paused"
    STOPPED = "stopped"
    
    
    def __init__(self,source):
        self.source = source
        
        transitions = [
            
            {"trigger":"play","source":self.PAUSED, "dest":self.PLAYING},
            {"trigger":"play","source":self.STOPPED, "dest":self.PLAYING},
            ##
            {"trigger":"pause","source":self.PAUSED, "dest":self.PAUSED},
            ##
            {"trigger":"stop","source":self.PAUSED, "dest":self.STOPPED},
            {"trigger":"stop","source":self.PLAYING, "dest":self.STOPPED}
            
        ]
        
        self.machine = Machine( 
        model = self,
        transitions = transitions,
        initial = self.STOPPED)
        
        
    def pause(self):
        print ("pause")
        
    def play(self):
        print ("play")
        
    def stop(self):
        print ("stop")

但我称之为，它不起作用：

test = Video("some text")

返回警告：

2020-09-27 17:25:50,255 [11472] WARNING  transitions.core:828: [JupyterRequire] Model already contains an attribute 'play'. Skip binding.
2020-09-27 17:25:50,259 [11472] WARNING  transitions.core:828: [JupyterRequire] Model already contains an attribute 'pause'. Skip binding.
2020-09-27 17:25:50,260 [11472] WARNING  transitions.core:828: [JupyterRequire] Model already contains an attribute 'stop'. Skip binding.

但主要问题是状态没有改变：

这是原演讲的代码：

【问题讨论】：

标签： python fsm

【解决方案1】：

我在这里发布修改后的代码，它会为您提供预期的输出。为代码格式化道歉，我真的很挣扎这里的标记编辑器。

有问题的代码似乎缺少的东西是

您没有将状态列表传递给 FSM 机器。

此外，看起来，机器使用触发功能修改模型。您拥有相同命名的函数似乎覆盖了那些[1]。我认为触发任何函数的正确方法是使用“after”属性和函数名称。很可能以前也会有。

from transitions import Machine

class Video:

    ## Define the states
    PLAYING = "playing"
    PAUSED = "paused"
    STOPPED = "stopped"

    states = [PLAYING, PAUSED, STOPPED]


    def __init__(self,source):
        self.source = source

        transitions = [ 

            {"trigger":"play","source":self.PAUSED, "dest":self.PLAYING, "after": "log_play"},
            {"trigger":"play","source":self.STOPPED, "dest":self.PLAYING, "after": "log_play"},
             ##  
            {"trigger":"pause","source":self.PAUSED, "dest":self.PAUSED},
            ##  
            {"trigger":"stop","source":self.PAUSED, "dest":self.STOPPED},
            {"trigger":"stop","source":self.PLAYING, "dest":self.STOPPED}

        ]   

        self.machine = Machine( 
            model = self,
            transitions = transitions,
            states = self.states,
            initial = self.STOPPED)


    def log_pause(self):
        print ("pause")

    def log_play(self):
        print ("play")

    def log_stop(self):
        print ("stop")

参考：

https://github.com/pytransitions/transitions/blob/master/transitions/core.py#L594

【讨论】：