'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.'

@staticmethod
def possible_string_format_functions(format_):

    (yield (lambda format_, val: format(val.value, format_)))
    (yield (lambda format_, val: format_.format(val.value)))
    (yield (lambda format_, val: (format_ % val.value)))
