python - 如何在 Python 中正确排序对象列表

Question

有一个位置类

class Location(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y
    def move(self, deltaX, deltaY):
        return Location(self.x + deltaX, self.y + deltaY)
    def getX(self):
        return self.x
    def getY(self):
        return self.y
    def dist_from(self, other):
        xDist = self.x - other.x
        yDist = self.y - other.y
        return (xDist**2 + yDist**2)**0.5
    def __eq__(self, other):
        return (self.x == other.x and self.y == other.y)
    def __str__(self):
        return '<' + str(self.x) + ',' + str(self.y) + '>'

还有一个 get_cars 方法，我根据以下规范编写该方法以从列表中检索数据(不属于 LOcation 类):

def get_cars(self):
    """ Returns a list of all cars on the parking. The list should contain 
    the string representation of the Location of a car. The list should 
    be sorted by the x coordinate of the location. """


    result = ''
    for i in sorted(self.car_loc_list, key=lambda Location: Location.x):
        if self.car_loc_list[0] == i:
            result += '\'' + str(i) + '\''
        else:    
            result += ', ' + '\'' + str(i) + '\''

    return '[' + result + ']'

self.car_loc_list 只是一个包含 Location 类 对象的列表，它们包含一些坐标 (x,y)(未排序):

for i in c.car_loc_list:
    print(i)

<0,0>
<1,5>
<7,2>
<2,1>
<1,7>
<4,3>

在线评分器以两种方式检查我的代码:

1. print(c.get_cars()) - 确定
2. print(sorted(c.get_cars())) - 不行

当我按照第一种方式时:

print(c.get_cars())

它打印出按 X 坐标(第 1 位)排序的下一个结果:

print(c.get_cars())
Out[539]: "['<0,0>', '<1,5>', '<1,7>', '<2,1>', '<4,3>', '<7,2>']"

这也是我(和评分者)期望得到的结果。

当我执行 print(sorted(c.get_cars)) 时，我得到:

print(sorted(c.get_cars()))
[' ', ' ', ' ', ' ', ' ', "'", "'", "'", "'", "'", "'", "'", "'", "'", "'", "'", "'", ',', ',', ',', ',', ',', ',', ',', ',', ',', ',', ',', '0', '0', '1', '1', '1', '2', '2', '3', '4', '5', '7', '7', '<', '<', '<', '<', '<', '<', '>', '>', '>', '>', '>', '>', '[', ']']

我卡在了这个地方。我也明白它以某种方式再次将我的输出转换为字符串，这就是为什么我得到这样的结果。是否有任何想法如何实现，以便两种解决方案根据上述规范给出相同的结果，例如 ['<0,0>', '<1,5>', '<1,7>', '<2,1>', '<4,3>', '<7,2>'] ？

UPD 下一句好像没听懂:

The list should contain the string representation of the Location of a car.

Answer 1

你的方法的描述很清楚你哪里出错了:

""" Returns a list of all cars on the parking. The list should contain 
the string representation of the Location of a car. The list should 
be sorted by the x coordinate of the location. """

您没有返回列表。您正在返回一个字符串，其内容看起来像一个列表。这不是一回事。

返回一个列表:

def get_cars(self):
    """ Returns a list of all cars on the parking. The list should contain 
    the string representation of the Location of a car. The list should 
    be sorted by the x coordinate of the location. """

    result = []
    for loc in sorted(self.car_loc_list, key=lambda loc: loc.x):
        result.append(str(loc))
    return result

或更简单地使用列表理解:

def get_cars(self):
    """ Returns a list of all cars on the parking. The list should contain 
    the string representation of the Location of a car. The list should 
    be sorted by the x coordinate of the location. """

    return [str(loc) for loc in sorted(self.car_loc_list, key=lambda loc: loc.x)]