old_contents: from flask import Flask, render_template
  
  app = Flask(__name__)
  
  
  @app.route('/')
  def hello():
      return render_template('hello.html')
  
new_contents: from flask import Flask, render_template
  
  app = Flask(__name__)
  
  
  @app.route('/')
  def hello():
      return render_template('hello.html')
  
  if __name__ == '__main__':
      app.run()
  
subject: Allow running the app from cli