title: How to check if apscheduler is running in the background
body: <p>I have a button that sends:</p>
  
  <pre><code>scheduler.start()
  </code></pre>
  
  <p>and would like to check whether it is running already to avoid <em>SchedulerAlreadyRunningError</em></p>
  
  <p>It seems simple enough but couldn't find a status flag in the documentation.</p>