text: from casbin import persist
  import os
  
  
  class FileAdapter(persist.Adapter):
      """the file adapter for Casbin.
      It can load policy from file or save policy to file.
      """
  
      _file_path = ""
  
      def __init__(self, file_path):
          self._file_path = file_path
  
      def load_policy(self, model):
          if not os.path.isfile(self._file_path):
              raise RuntimeError("invalid file path, file path cannot be empty")
  
          self._load_policy_file(model)
  
      def save_policy(self, model):
          pass
  
      def _load_policy_file(self, model):
          with open(self._file_path, "rb") as file:
              line = file.readline()
              while line:
                  persist.load_policy_line(line.decode().strip(), model)
                  line = file.readline()
  
      def _save_policy_file(self, text):
          pass
  
      def add_policy(self, sec, ptype, rule):
          pass
  
      def remove_policy(self, sec, ptype, rule):
          pass
  
      def remove_filtered_policy(self, sec, ptype, field_index, *field_values):
          pass
  