title: Python flask route: what does '?' mean in the end of rule?
body: <p>I have encountered the following piece of code in a flask project:</p>
  
  <pre><code>@app.route(r"^/subscriptions/?")
  class SubscriptionsHandler:
      ...
  </code></pre>
  
  <p>I am not sure what the '?' symbol in the end of route pattern means?</p>
  
  <p>I've checked docs and several tutorials but have not found similar route examples.</p>