old_contents: import os
  
  from flask import Flask
  app = Flask(__name__)
  
  @app.route("/")
  def hello():
      return "Hello World!"
  
  if __name__ == "__main__":
      app.run(
          port=int(os.environ.get('PORT', 5000))
      )
  
new_contents: import os
  
  from flask import Flask
  app = Flask(__name__)
  
  @app.route("/")
  def hello():
      return "Hello World!"
  
  if __name__ == "__main__":
      app.run(
          host="0.0.0.0",
          port=int(os.environ.get('PORT', 5000))
      )
  
subject: Fix error when running python sample on codebox.io