如何从PyTransitions有限状态机生成输出？

Question

我正在使用PyTransitions生成一个简单的有限状态机，并使用一个yml文件对其进行配置。示例可能如下所示：

initial: A
states:
  - A
  - B
  - C
transitions:
  - {trigger: "AtoC", source: "A", dest: "C"}
  - {trigger: "CtoB", source: "C", dest: "B"}

我的问题是，使用yml文件，我如何在状态输出中写入？例如，在状态A打开LED1，状态B打开LED2，状态C打开LED1和2。我在PyTransitions页面中找不到任何文档。

Answer 1

我的问题是，使用yml文件，我如何在状态输出中写入？

状态没有专用的输出槽，但您可以使用transitions在进入或离开状态时触发某些操作。操作可以在回调中完成。这些操作需要在模型中实现。如果你想通过配置来做大多数事情，你可以定制Machine和使用的State类。例如，您可以创建一个自定义发光二极管，并为其分配一个名为led_states的值数组，其中每个值表示一个LEDState状态。该数组应用于名为update_leds的模型的after_state_change回调中的LED

from transitions import Machine, State


class LEDState(State):

    ALL_OFF = [False] * 2  # number of LEDs

    def __init__(self, name, on_enter=None, on_exit=None,
                 ignore_invalid_triggers=None, led_states=None):
        # call the base class constructor without 'led_states'...
        super().__init__(name, on_enter, on_exit, ignore_invalid_triggers)
        # ... and assign its value to a custom property
        # when 'led_states' is not passed, we assign the default 
        # setting 'ALL_OFF'
        self.led_states = led_states if led_states is not None else self.ALL_OFF

# create a custom machine that uses 'LEDState'
# 'LEDMachine' will pass all parameters in the configuration
# dictionary to the constructor of 'LEDState'.
class LEDMachine(Machine):
   
    state_cls = LEDState


class LEDModel:

    def __init__(self, config):
        self.machine = LEDMachine(model=self, **config, after_state_change='update_leds')

    def update_leds(self):
        print(f"---New State {self.state}---")
        for idx, led in enumerate(self.machine.get_state(self.state).led_states):
            print(f"Set LED {idx} {'ON' if led else 'OFF'}.")

# using a dictionary here instead of YAML
# but the process is the same
config = {
    'name': 'LEDModel',
    'initial': 'Off',
    'states': [
        {'name': 'Off'},
        {'name': 'A', 'led_states': [True, False]},
        {'name': 'B', 'led_states': [False, True]},
        {'name': 'C', 'led_states': [True, True]}
    ]
}

model = LEDModel(config)
model.to_A()
# ---New State A---
# Set LED 0 ON.
# Set LED 1 OFF.
model.to_C()
# ---New State C---
# Set LED 0 ON.
# Set LED 1 ON.

这只是实现此目的的一种方法。您也可以只传递一个数组，该数组包含表示所有LED的索引，这些LED应该为ON。当使用before_state_change退出状态时，我们会关闭所有LED

ALL_OFF = []

#  ...

self.machine = LEDMachine(model=self, **config, before_state_change='reset_leds', after_state_change='set_lets')

# ...

 def reset_leds(self):
    for led_idx in range(num_leds):
        print(f"Set {led_idx} 'OFF'.")

 def set_lets(self):
    for led_idx in self.machine.get_state(self.state).led_states:
        print(f"Set LED {led_idx} 'ON'.")
# ...

    {'name': 'A', 'led_states': [0]},
    {'name': 'B', 'led_states': [1]},
    {'name': 'C', 'led_states': [0, 1]}