new_contents: import asyncio
  import logging
  
  import aiohttp
  import backoff
  
  
  @backoff.on_exception(backoff.expo,
                        aiohttp.errors.ClientError,
                        max_tries=8)
  async def get_url(url):
      async with aiohttp.ClientSession() as session:
          async with session.get(url) as response:
              return await response.text()
  
  @backoff.on_exception(backoff.expo,
                        aiohttp.errors.ClientError,
                        max_tries=8)
  @asyncio.coroutine
  def get_url_py34(url):
      with aiohttp.ClientSession() as session:
          response = yield from session.get(url)
          try:
              return (yield from response.text())
          except Exception:
              response.close()
              raise
          finally:
              yield from response.release()
  
  
  format_string = '%(asctime)-15s %(name)s %(levelname)s: %(message)s'
  logging.basicConfig(format=format_string, level=logging.DEBUG)
  
  url = 'http://python.org/'
  #url = 'http://localhost:34534/'
  
  loop = asyncio.get_event_loop()
  print(loop.run_until_complete(get_url_py34(url))[:100])
  print(loop.run_until_complete(get_url(url))[:100])
  
subject: Add backoff retry async example