class_docstr: Simple event to which event handlers can be attached. For instance::
  
      class Cls:
          def __init__(self):
              # Define event. The first parameter is the sender.
              self.event = Event(self)
  
      obj = Cls()
  
      def handler(sender):
          pass
  
      # Add event handler by using the += operator.
      obj.event += handler
  
      # Fire event.
      obj.event()
code: def __init__(
      self,
      sender: _Sender,
      handler: Callable[[_Sender], None] | None = None,
  ) -> None:
      self.sender = sender
      self._handlers: list[Callable[[_Sender], None]] = []
  
      if handler is not None:
          self += handler
  
imports: from __future__ import annotations
  import os
  import signal
  import sys
  import threading
  from collections import deque
  from typing import Callable, ContextManager, Dict, Generator, Generic, TypeVar, Union
  from wcwidth import wcwidth
label_desc: Use image node_id 1 to create a new Event object from inherited base classes: Generic with example: obj = Event(sender, handler)