title: Python: wait for requests_futures.sessions to finish before continuing with the code flow
body: <p>My current code as it stands prints an empty list, how do I wait for all requests and callbacks to finish before continuing with the code flow? </p>
  
  <pre><code>from requests_futures.sessions import FuturesSession
  from time import sleep
  
  session = FuturesSession(max_workers=100)
  
  i = 1884001540 - 100
  list = []
  def testas(session, resp):
      print(resp)
      resp = resp.json()
      print(resp['participants'][0]['stats']['kills'])
      list.append(resp['participants'][0]['stats']['kills'])
  while i &lt; 1884001540:
      url = "https://acs.leagueoflegends.com/v1/stats/game/NA1/" + str(i)
      temp = session.get(url, background_callback=testas)
      i += 1
  print(list)
  </code></pre>