code: def _update(self, flag):
      self._modified = False
      self._index = {}
      try:
          f = _io.open(self._dirfile, "r", encoding="Latin-1")
      except OSError:
          if flag not in ("c", "n"):
              raise
          self._modified = True
      else:
          with f:
              for line in f:
                  line = line.rstrip()
                  key, pos_and_siz_pair = _ast.literal_eval(line)
                  key = key.encode("Latin-1")
                  self._index[key] = pos_and_siz_pair
  
imports: import ast
  import io
  import os
  import collections.abc
label_desc: Use image node_id 3 for calling the _Database obj's underlying member method code with example usage: obj._update(flag) without return types