title: Threading object issue
body: <p>I can't figure out why the threading object <code>threadObj</code> can't use <code>isAlive</code>, when I call <code>stop()</code>. The code is described below.</p>
  
  <pre><code>from threading import Thread
  
  class workerThread(Thread):
    def __init__(self, _parent):
      Thread.__init__(self)
      self.parent = _parent
      self.active = False
  
    def run(self):
      while(self.active == False):
        print 'I am here'
      print 'and now I am here'
  
  class imp():
    def __init__(self):
      self.threadObj = None
  
    def start(self):
      self.threadObj = workerThread(self)
      self.threadObj.start()
  
    def stop(self):
      if self.threadObj.isAlive() == True:
        print 'it is alive'
  </code></pre>
  
  <p>It says: AttributeError: 'NoneType' object has no attribute 'isAlive'</p>
  
  <p>The calling code is descibed below:</p>
  
  <pre><code>from filename import imp
  
  filename = imp()
  if option == 'A':
    filename.start()
  elif option == 'B':
    filename.stop()
  </code></pre>