code: def CreatePrecisionHelper(cls, precision):
      
      precision_helper_class = cls._PRECISION_CLASSES.get(precision, None)
      if not precision_helper_class:
        raise ValueError('Unsupported precision: {0!s}'.format(precision))
  
      return precision_helper_class
docs: Creates a precision helper.
  
      Args:
        precision (str): precision of the date and time value, which should
            be one of the PRECISION_VALUES in definitions.
  
      Returns:
        class: date time precision helper class.
  
      Raises:
        ValueError: if the precision value is unsupported.