old_contents: import dj_database_url
  
  DATABASES = {
      'default': dj_database_url.config()
  }
  
  ALLOWED_HOSTS = ['.herokuapp.com']
  
  DEBUG = False
  
new_contents: import dj_database_url
  
  DATABASES = {
      'default': dj_database_url.config()
  }
  
  ALLOWED_HOSTS = ['.herokuapp.com']
  
subject: use env variable to decide DEBUG or not on heroku