Question

我试图模仿以下产出(来自Marakana.com s excellent Python 教程 ):

>>> for c in lot.cars_by_age():
...     print c
1981 VW Vanagon
1988 Buick Regal
2010 Audi R8

到目前为止,我的代码是:

class ParkingLot(object):
    def __init__(self, spaces, cars=[]):
        self.spaces = spaces
        self.cars = cars
    def park(self, car):
        if self.spaces == 0:
            print "The lot is full."
        else:
            self.spaces -= 1
            self.cars.append(car)
    def __iter__(self):
        return (car for car in self.cars)

class Car(object):
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
    def __str__(self):
        return  %s %s %s  % (car.year, car.make, car.model)

我想在“泊车 Lot () ” 类中添加一种方法( cars_ by_ age () ) 。但是, 根据样本代码, 此方法需要某种可操作性。我不知道该如何操作 - 对于一个类, 您定义一个 < enger > iter < / strong > 函数, 但是对于一种方法, 您如何定义此方法?

Answer 1

并不是说 ethod 是可行的;使用该方法返回的值是可行的。执行 cars_by_age 可能只是返回一个 Car 列表。

def cars_by_age(self):
    return sorted(self.cars, key=lambda car: car.year)

使用 < a href=" "http://docs.python.org/library/forms.html#sorded" rel="noreferrer"\\ code>sorded 创建一个新的分类列表,并使用 < a href=> code>lambda 来指定您想要按照汽车的 S year 属性排序。

http://wiki.python.org/moin/HowTo/Sorting" rel=“noreferrer'>http://wiki.python.org/moin/HowTo/Sorting

Answer 2

from operator import attrgetter

class ParkingLot(object):
    def __init__(self, spaces, cars=None):
        self.spaces = max(spaces, 0)
        self.cars = cars or []
    def park(self, car):
        if self.spaces > 0:
            self.spaces -= 1
            self.cars.append(car)
        else:
            print "The lot is full."
    def __iter__(self):
        return iter(self.cars)
    def cars_by_age(self):
        return sorted(self.cars, key=attrgetter("year"), reverse=True)

class Car(object):
    def __init__(self, make, model, year):
        self.make = make
        self.model = model
        self.year = year
    def __str__(self):
        return "{} {} {}".format(self.year, self.make, self.model)

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