code: def is_file(self):
      if self._is_file is None:
          if self.is_dir() or not oss_exists(self._path):
              self._is_file = False
          else:
              self._is_file = True
      return self._is_file
  
imports: import base64
  import json
  import os
  from ..base import path_type, stringify_path
  from ....utils import lazy_import
label_desc: Use image node_id 3 for calling the OSSFileEntry obj's underlying member method code with example usage: obj.is_file() and returns: self