code: def normalize_data_format(value):
      if value is None:
          value = backend.image_data_format()
      data_format = value.lower()
      if data_format not in {"channels_first", "channels_last"}:
          raise ValueError(
              "The `data_format` argument must be one of "
              '"channels_first", "channels_last". Received: '
              + str(value)
          )
      return data_format
  
file_path: tensorflow/tensorflow/python/keras/utils/conv_utils.py
imports: import itertools
  import numpy
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.keras import backend
  from tensorflow.python.ops import array_ops
label_desc: Use image node_id 6 for calling a global function with example usage: normalize_data_format(value) and returns: data_format