实用工具状态机transitions
2020年11月21日 09:42
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
