Async timer with callback

async_timer.py

import asyncio
from asyncio import Future
from collections import Callable
from typing import ClassVar
from typing import Optional


class Timer:
  _task: Optional[ Future ] = None
  _timeout: ClassVar[ float ]
  _callback: ClassVar[ Callable ]

  def __init__ ( self, timeout, callback ):
    self._timeout = timeout
    self._callback = callback

  async def _job ( self ):
    await asyncio.sleep( self._timeout )
    await self._callback()

  def start ( self ):
    self._task = asyncio.ensure_future( self._job() )

  def cancel ( self ):
    if self._task is not None:
      self._task.cancel()