About Python Event Emitter

This is a python implementation for JavaScript-like EventEmitter class

Usage

If you want that your class use a JavaScript-like on() and emit() approaches for event handling, just extends your class with EventEmitter class just the same as you do in JavaScript

Example

fromevent_emitterimportEventEmitterclassMyEventClass(EventEmitter):
def__init__(self):
super().__init__()
print("This is a EventEmitter example")
self.on("my-event", lambdavalue: print(f"my-event got value: {value}"))
if__name__=="__main__":
event_example=MyEventClass()
event_example.emit("my-event", "Test")

Classes

EventEmitter

This is your base class for your event-based class. This is the one that implements EventEmitter JavaScript-like class with on and emit methods for handling and emitting events.

EventHandler

This is a container for events callback you can add or remove functions by using append and remove methods or += and -=* operator. It is an iterable object, so you can iterate through it to get all callback functions. It is also a callable object, so if you want to call all functions, just call this EventHandler instance object, this is the way how EventEmitter run callback functions when an event happens

Example

fromevent_emitterimportEventHandlerhandler=EventHandler()
handler+=lambdalabel: print(f"First callback of f{label}")
handler+=lambdalabel: print(f"Second callback of f{label}")
handler+=lambdalabel: print(f"Third callback of f{label}")
handler("test")

EventCallable

This is a wrapper for event callback. This class implements an once static method decorator for handling once-call event handler, you can pass an asyncio event loop object to loop parameter in case of using an async function and you want to execute it on a event loop different from your current event loop.

Example

fromevent_emitterimportEventCallable, EventEmitterevent_example=EventEmitter()
@EventCallable.once(event_example, "test")defcallback(label):
print(f"Event called with label: {label}")
event_example.on("test", callback)
event_example.emit("test", "First call")
event_example.emit("test", "Second call")

Internals

Event Handling

All events of EventEmitter class is execute on a separate thread to avoid event processing to block your application main thread. If your event handler is a coroutine then it is executed on your current event loop. If you want to use a different event loop, then you must use a EventCallable class for your event callback and pass a different event loop object to it's argument