title: Deferred callback not being called using Python requests-threads
body: <p>I am trying to perform async HTTP requests by using the requests library in Python. I found that the last version of the library does not directly support async requets. To achive it they provide the requests-threads library that makes use of Twisted to handle asynchronicity. I tried modifying the examples provided to use callbacks instead of await/yield, but the callbacks are not being called. </p>
  
  <p>My sample code is:</p>
  
  <pre><code>session = AsyncSession(n=10)
  
  def processResponse(response):
    print(response)
  
  def main():
    a = session.get('https://reqres.in/api/users')
    a.addCallbacks(processResponse, processResponse)
    time.sleep(5)
  </code></pre>
  
  <p>The requests-threads library: <a href="https://github.com/requests/requests-threads" rel="nofollow noreferrer">https://github.com/requests/requests-threads</a></p>