code: def _find_channel_index(data_format):
    
    for i, c in enumerate(data_format):
      if c == "C":
        return i
    raise ValueError("data_format requires a channel dimension. Got: {}"
                     .format(data_format))
docs: Returns the index of the channel dimension.
  
    Args:
      data_format: A string of characters corresponding to Tensor dimensionality.
  
    Returns:
      channel_index: An integer indicating the channel dimension.
  
    Raises:
      ValueError: If no channel dimension was found.