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()
docstr: `event -= handler` notation for removing a handler.
code: def __isub__(
      self, handler: Callable[[_Sender], None]
  ) -> Event[_Sender]:
      """
      `event -= handler` notation for removing a handler.
      """
      self.remove_handler(handler)
      return self
  
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 7 for calling the Event obj's underlying member method code with example usage: obj.__isub__(handler) and returns: self