在 Python 中存储回调函数的值

Question

我正在尝试存储回调函数的内容，以便在脚本中访问和操作数据。就我而言，下面代码中的给定函数 .subscribe() 没有 return 任何东西 (None)。我的函数仅作为函数的引用作为参数传递。有没有办法 return 来自调用我函数的函数的数据？

我的代码是 roslibpy 的一个简单示例（与开源机器人框架 交互的 Python 库ROS 通过 Websockets）。有人提到，每次将消息发布到主题 /turtle1/pose 时，数据都会通过 Websocket 作为流发布。我的目标是 return 将发布到主题中的数据。打印命令提供了一个很好的数据可视化效果，效果很好。

import roslibpy
  
client = roslibpy.Ros(host='localhost', port=9090)
client.run()

def myfunc(msg):
    print(msg)
      
listener = roslibpy.Topic(client, '/turtle1/pose', 'turtlesim/Pose')

#my function is passed as an argument
listener.subscribe(myfunc)

try:
    while True:
         pass
except KeyboardInterrupt:
    client.terminate()

roslibpy库中的subscribe()方法定义如下：

def subscribe(self, callback):
    """Register a subscription to the topic.

    Every time a message is published for the given topic,
    the callback will be called with the message object.

    Args:
        callback: Function to be called when messages of this topic are published.
    """
    # Avoid duplicate subscription
    if self._subscribe_id:
        return

    self._subscribe_id = 'subscribe:%s:%d' % (
        self.name, self.ros.id_counter)

    self.ros.on(self.name, callback)
    self._connect_topic(Message({
        'op': 'subscribe',
        'id': self._subscribe_id,
        'type': self.message_type,
        'topic': self.name,
        'compression': self.compression,
        'throttle_rate': self.throttle_rate,
        'queue_length': self.queue_length
    }))

是否有处理此类问题的通用方法？将输出存储为外部源（例如 .txt）然后通过脚本访问源是否更有意义？

Answer 1

您可以定义一个像函数一样运行的 Python class，通过定义神奇的 __call__ 方法，它可以在调用时修改自己的状态。当 obj(whatever) 在非函数 obj 上完成时，Python 将运行 obj.__call__(whatever)。 subscribe 只需要它的输入是可调用的；它是实际函数还是具有 __call__ 方法的对象与 subscribe.

无关

这是您可以执行的操作的示例：

class MessageRecorder():
    def __init__(self):
        self.messages = []

    # Magic python 'dunder' method
    # Whenever a MessageRecorder is called as a function
    # This function defined here will be called on it
    # In this case, adds the message to a list of received messages
    def __call__(self, msg):
        self.messages.append(msg)

recorder = MessageRecorder()

# recorder can be called like a function
recorder("Hello")

listener.subscribe(recorder)

try:
    while True:
         pass
except KeyboardInterrupt:
    client.terminate()

"""Now you can do whatever you'd like with recorder.messages,
which contains all messages received before termination,
in order of reception. If you wanted to print all of them, do:"""
for m in recorder.messages:
    print(m)

在 Python 中存储回调函数的值

Store value of a callback function in Python

python

callback

ros