old_contents: class Backend(object):
      def __init__(self, plugin, params):
          self._plugin = plugin
          self._params = params
          self._categories = []
          
      @property
      def plugin(self):
          return self._plugin
      
      @property
      def params(self):
          return self._params
          
      def add_category(self, category):
          self._categories.append(category)
      
new_contents: class Backend(object):
      def __init__(self, plugin, params):
          self._plugin = plugin
          self._params = params
          self._categories = []
          
      @property
      def plugin(self):
          return self._plugin
      
      @property
      def params(self):
          return self._params
          
      def add_category(self, category):
          self._categories.append(category)
      
  
subject: Update parse so it doesn't return anything, just stores objects locally. Lots of tidying