old_contents: from flask import Flask
  
  app = Flask(__name__)
  
  @app.route('/')
  def index():
      return 'hello world!'
  
new_contents: from flask import Flask
  
  app = Flask(__name__, static_path='/public')
  
  @app.route('/')
  def index():
      return 'hello world!'
  
  if __name__ == '__main__':
      app.run(debug=True)
  
subject: Make app run in dev mode