python 实用工具状态机transitions

说明 

1. 状态机是一个非常实用的理论。在涉及到复杂的场景，建立状态机模型，能带来极大的方便。比如，网络连接、模型状态、业务逻辑。 
2. 状态机并不复杂, 重要的是它的思想，能够极大减轻复杂度。使用时关键在于定义好事件和动作。 

基本概念 

State: 状态 Event: 事件. 事件触发状态变换 Action: 动作. event发生前或后执行的动作 transition: 变换. 状态变换

github

https://github.com/pytransitions/transitions

安装

pip install transitions

简单示例

# 连接协议状态机
from transitions.extensions import HierarchicalMachine as Machine
from transitions.extensions.nesting import NestedState
 
class ConnectionStateMachine:
    \"\"\"Connection state machine.\"\"\"
 
    def __init__(self, callbacks=None):
        \"\"\"
        :param callbacks: callbacks for the state machine
        \"\"\"
        self.callbacks = {}
 
        # 定义状态
        self.states = [\"STATE_NOT_CONNECTED\",
                       {
                            \'name\': \"STATE_CONNECTED\",   # 状态名
                            \'on_enter\': self._on_enter_CONNECTED,  # 进入状态触发
                            \'on_exit\': self._on_exit_CONNECTED,    # 退出状态触发
                            \'children\': [     # 状态嵌套
                                \"STATE_NOT_SELECTED\",
                                {
                                    \'name\': \"STATE_SELECTED\",
                                    \'on_enter\': self._on_enter_CONNECTED_SELECTED
                                }
                            ]
                       }]
 
        # transition 1
        self.machine = Machine(model=self, states=self.states, initial=\"STATE_NOT_CONNECTED\", auto_transitions=False)
 
        if callbacks:
            self.callbacks = callbacks
 
        # 定义状态变换
        self.machine.add_transition(\'connect\', \"STATE_NOT_CONNECTED\", \"STATE_CONNECTED_NOT_SELECTED\")  # transition 2
        self.machine.add_transition(\'disconnect\', \"STATE_CONNECTED\", \"STATE_NOT_CONNECTED\")  # transition 3
        self.machine.add_transition(\'select\', \"STATE_CONNECTED_NOT_SELECTED\", \"STATE_CONNECTED_SELECTED\")  # transition 4
        self.machine.add_transition(\'deselect\', \"STATE_CONNECTED_SELECTED\", \"STATE_CONNECTED_NOT_SELECTED\")  # transition 5
        self.machine.add_transition(\'timeoutT7\', \"STATE_CONNECTED_NOT_SELECTED\", \"STATE_NOT_CONNECTED\")  # transition 6
 
    # 事件触发的动作
    def _on_enter_CONNECTED(self):
        if \"on_enter_CONNECTED\" in self.callbacks:
            self.callbacks[\"on_enter_CONNECTED\"]()
 
    def _on_exit_CONNECTED(self):
        if \"on_exit_CONNECTED\" in self.callbacks:
            self.callbacks[\"on_exit_CONNECTED\"]()
 
    def _on_enter_CONNECTED_SELECTED(self):
        if \"on_enter_CONNECTED_SELECTED\" in self.callbacks:
            self.callbacks[\"on_enter_CONNECTED_SELECTED\"]()

定义状态机

# 一般都是两种：不嵌套、嵌套
from transitions import Machine   #不嵌套
from transitions.extensions import HierarchicalMachine as Machine # 嵌套
 
# 检查状态
machine.state
machine.is_<state_name>()

定义状态

# 状态可以是三种类型: 对象、字符串、字典
from transitions import State
states = [
    State(name=\"solid\"),    # 对象
    \"liquid\",               # 字符串
    {\"name\": \"gas\"}         # 字典
]

定义变换

# 定义函数
machine.add_transition(trigger, source, dest, )
trigger(str)         方法名,触发状态转换
source(str or list)  源状态
dest(str)            目标状态
 
# 加上变换
machine.add_transition(trigger=\"wake_up\", source=\"asleep\", dest=\"hanging out\")
machine.add_transition(\'work_out\', \'hanging out\', \'hungry\')
machine.add_transition(\'nap\', \'*\', \'asleep\')   # 从任意状态变为asleep

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