title: There's invalid syntax in pub.py
body: <p>The followed method is defined in the pubsub.py which is a python file in the site-package pubsub. When I try to use this, the pycharm tells me this is invalid syntax with an arrow pointing to '->'. I don't why and I have installed the pypubsub.</p>
  
  <pre><code>def getDefaultPublisher() -> Publisher:
      """
      Get the Publisher instance created by default when this module
      is imported. See the module doc for details about this instance.
      """
      return _publisher</code></pre>