fuel.py 文件源码

def calculate_mpg(self):
        """
        Calculate ``calculated_mpg`` field.

        :returns: True if recalculate, False if unable to calculate
        :rtype: bool
        """
        if self.gallons is None:
            logger.warning(
                'Gallons is none; cannot recalculate MPG for %s', self
            )
            return False
        if self.odometer_miles is None:
            logger.warning(
                'odometer_miles is none; cannot recalculate MPG for %s', self
            )
            return False
        prev = self._previous_entry()
        if prev is None:
            logger.warning('Previous entry is None; cannot recalculate MPG '
                           'for %s', self)
            return False
        distance = self.odometer_miles - prev.odometer_miles
        self.calculated_miles = distance
        self.calculated_mpg = (
            (distance * Decimal(1.0)) / self.gallons
        ).quantize(Decimal('.001'), rounding=ROUND_FLOOR)
        logger.debug('Calculate MPG for fill %d: distance=%s mpg=%s',
                     self.id, distance, self.calculated_mpg)
        inspect(self).session.add(self)