Class Event

core/src/stdlib/pyscript/events.py:23–84

A custom event that can notify multiple listeners when triggered. Use this class to create your own event system within Python code. Listeners can be either regular functions or async functions. ```python from pyscript.events import Event # Create a custom event. data

class Event:
    """
    A custom event that can notify multiple listeners when triggered.

    Use this class to create your own event system within Python code.
    Listeners can be either regular functions or async functions.

    ```python
    from pyscript.events import Event

    # Create a custom event.
    data_loaded = Event()

    # Add a listener.
    def on_data_loaded(result):
        print(f"Data loaded: {result}")

    data_loaded.add_listener(on_data_loaded)

    # Time passes.... trigger the event.
    data_loaded.trigger({"data": 123})
    ```
    """

    def __init__(self):
        self._listeners = []

    def trigger(self, result):
        """
        Trigger the event and notify all listeners with the given `result`.
        """
        for listener in self._listeners:
            if is_awaitable(listener):
                asyncio.create_task(listener(result))
            else:
                listener(result)

    def add_listener(self, listener):
        """
        Add a function to be called when this event is triggered.

        The `listener` must be callable. It can be either a regular function
        or an async function. Duplicate listeners are ignored.
        """
        if not callable(listener):
            msg = "Listener must be callable."
            raise ValueError(msg)
        if listener not in self._listeners:
            self._listeners.append(listener)

    def remove_listener(self, *listeners):
        """
        Remove specified `listeners`. If none specified, remove all listeners.
        """
        if listeners:
            for listener in listeners:
                try:
                    self._listeners.remove(listener)