def DeregisterFormatter(cls, formatter_class):
    """Deregisters a formatter class.

    The formatter classes are identified based on their lower case data type.

    Args:
      formatter_class (type): class of the formatter.

    Raises:
      KeyError: if formatter class is not set for the corresponding data type.
    """
    formatter_data_type = formatter_class.DATA_TYPE.lower()
    if formatter_data_type not in cls._formatter_classes:
      raise KeyError(
          'Formatter class not set for data type: {0:s}.'.format(
              formatter_class.DATA_TYPE))

    del cls._formatter_classes[formatter_data_type]