使用过渡库，状态不会在python中的FSM中更改

编程问答 2022-06-11

问题描述

我正在尝试从此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,##
            {"trigger":"pause","dest":self.PAUSED},##
            {"trigger":"stop","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")

但是我称之为一个，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.

但是主要问题是状态不会改变：

enter image description here

这是原始演讲的代码：

enter image description here

enter image description here

解决方法

我将修改后的代码发布到此处，从而为您提供预期的输出。对代码格式表示歉意，我真的在这里使用标记编辑器。

有问题的代码似乎缺少的东西

  1. 您没有将状态列表传递给FSM计算机。

  2. 此外，机器看起来还具有触发功能。您具有相同的命名函数似乎会覆盖那些[1]。我认为触发任何功能的正确方法是使用“ after”属性和功能名称。 

    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,##  
            {"trigger":"pause","dest":self.PAUSED},##  
            {"trigger":"stop","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：

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