old_contents: from flask import Flask
  app = Flask(__name__)
  
  @app.route('/')
  def main():
      return 'ok'
  
  if __name__ == '__main__':
      app.run()
  
new_contents: from flask import Flask
  app = Flask(__name__)
  
  @app.route('/')
  def main():
      return 'ok'
  
  if __name__ == '__main__':
      app.debug = True
      app.run(host='0.0.0.0')
  
subject: make the server visible to the internet