title: What is the SyntaxError here in return '<h1>Hello world</h1>' when I try to launch my Flask application?
body: <p>I am a beginner at Flask and this is my first time trying to run a Flask application. My hello.py code is:</p>
  <pre><code>from flask import Flask
  app = Flask(__name__)
  @app.route('/')
  def index:
      return '&lt;h1&gt;Hello world&lt;/h1&gt;'
  </code></pre>
  <p>And after running the program on CMD using the command <code>python -m flask run</code></p>
  <p>I got this error</p>
  <pre><code>SyntaxError
  File &quot;C:\Users\91932\OneDrive\Desktop\Projects\Personal Projects\FLASK Projects\Test\hello.py&quot;, line 4
      def index:
               ^
  SyntaxError: invalid syntax
  </code></pre>
  <p>What should I do? Please help.</p>