code: def str_fraction(self):
          
          if self._eta.undefined:
              return None
  
          # Determine denominator and its unit.
          unit_denominator, unit = self._unit_class(self.denominator).auto
          formatter = '%d' if unit_denominator == self.denominator else '%0.2f'
          denominator = locale.format(formatter, unit_denominator, grouping=True)
  
          # Determine numerator.
          unit_numerator = getattr(self._unit_class(self.numerator), unit)
          if self.done:
              rounded_numerator = unit_numerator
          else:
              rounded_numerator = float(Decimal(str(unit_numerator)).quantize(Decimal('.01'), rounding=ROUND_DOWN))
          numerator = locale.format(formatter, rounded_numerator, grouping=True).rjust(len(denominator))
  
          return '{0}/{1} {2}'.format(numerator, denominator, unit)
docs: Returns the fraction with additional whitespace.