code: def __dir__(self):
      result = list(super().__dir__())
      if self.input.ndim == 1:
          return result
      else:
          return sorted(
              result
              + [
                  k
                  for k in self.input.dtypes.index
                  if isinstance(k, str) and k.isidentifier()
              ]
          )
  
file_path: mars/mars/dataframe/window/core.py
imports: from ...serialization.serializables import Serializable, KeyField
label_desc: Use image node_id 9 for calling the Window obj's underlying member method code with example usage: obj.__dir__() and returns: result, sorted