code: def data_format(self) -> str:
      if self._data_format is None:
          raise AttributeError(  # AttributeError -> hasattr returns False
              "please specify data_format when initializing the NumPyModel"
          )
      return self._data_format
  
file_path: foolbox/foolbox/models/numpy.py
imports: from typing import TypeVar, Callable, Optional
  import eagerpy
  from ..types import Bounds
  from ..types import BoundsInput
  from .base import Model
label_desc: Use image node_id 4 for calling the NumPyModel obj's underlying member method code with example usage: obj.data_format() and returns: self