old_contents: import flask
  
  app = flask.Flask(__name__)
  
  @app.route('/')
  def index():
      return flask.render_template('index.html')
  
  
  @app.route('/hello')
  def hello():
      return 'hello'
  
  if __name__ == '__main__':
      app.run(debug=True)
  
new_contents: import os
  import flask
  
  app = flask.Flask(__name__)
  
  @app.route('/')
  def index():
      return flask.render_template('index.html')
  
  
  @app.route('/hello')
  def hello():
      return 'hello'
  
  if __name__ == '__main__':
      port = int(os.environ.get("PORT", 5000))
      app.run(host='0.0.0.0', port=port, debug=True)
  
subject: Make app port configurable