title: Python Threads object append to list
body: <p>I am learning multi-thread in python.I often see when the program use multi thread,it will append the thread object to one list, just as following:</p>
  
  <pre><code># imports
  import threading
  import time
  
  def worker():
      print "worker...."
      time.sleep(30)
  
  threads = []
  for i in range(5):
      thread = threading.Thread(target=worker)
      threads.append(thread)
      thread.start()
  </code></pre>
  
  <p>I think append the thread object to list is good practice, but I don't know why should we do this?</p>