title: Simple Flask-SocketIo with "SyntaxError: invalid syntax"
body: <p>I'm following the Flask-SocketIo documentation (<a href="https://flask-socketio.readthedocs.io/en/latest/" rel="nofollow noreferrer">https://flask-socketio.readthedocs.io/en/latest/</a>) and the example code</p>
  <pre><code>from flask import Flask, render_template
  from flask_socketio import SocketIO
  
  app = Flask(__name__)
  app.config['SECRET_KEY'] = 'secret!'
  socketio = SocketIO(app)
  
  if __name__ == '__main__':
       socketio.run(app)
  </code></pre>
  <p>Is giving me this error:</p>
  <pre><code>    self.async = None
           ^
  SyntaxError: invalid syntax
  </code></pre>
  <p>Every thing is up-to-date, thus I think the error is from the official package. Does anyone know how to solve this?</p>