old_contents: from flask import Flask, render_template
  
  app = Flask(__name__)
  
  
  @app.route("/")
  def index():
      return render_template('home.html')
  
  
  if __name__ == "__main__":
      app.run(debug=True)
  
new_contents: import sys
  
  from flask import Flask, render_template
  
  app = Flask(__name__)
  
  
  @app.route("/")
  def index():
      return render_template('home.html')
  
  
  if __name__ == "__main__":
  	port = 8000
  	if len(sys.argv) >= 2:
  		port = int(sys.argv[1])
  	app.run(port=port, debug=True)
  
subject: choose port as a command line argument. (default: 8000)