@staticmethod
def possible_string_format_functions(format_):
    """Iterate through possible string-derived format functions.

        A string can either be a format specifier for the format built-in,
        a new-style format string, or an old-style format string.

        This method is overridden in order to suppress printing the unit
        in each row since it is already at the top in the column header.
        """
    yield lambda format_, val: format(val.value, format_)
    yield lambda format_, val: format_.format(val.value)
    yield lambda format_, val: format_ % val.value
