如何让__lt __()进行排序

Question

class City:
    def __init__(self, string):
        self._string = string.split(',')
        self._name = self._string[0]
        self._state = self._string[1]
        self._latitude = self._string[2]
        self._longitude = self._string[3]
        self._location = [self._latitude, self._longitude]

    def name(self):
        return self._name

    def location(self):
        return self._location
        self.hand.sort(key=lambda x: x.longitude)

    def __lt__(self, other):
        if self._longitude < other._longitude:
            return True
        if self._longitude > other._longitude:
            return False
        if self._longitude == other._longitude:
            if self._latitude < other._latitude:
                return True
            if self._latitude > other._latitude:
                return False

citystrings = ["Charleston,WV,38.35,81.63",
              "Charlotte,NC,35.23,80.83",
              "Cheyenne,WY,41.15,104.87",
              "Chicago,IL,41.83,87.62",
              "Cincinnati,OH,39.13,84.50",
              "Cleveland,OH,41.47,81.62",
              "Columbia,SC,34.00,81.03",
              "Columbus,OH,40.00,83.02",
              "Dallas,TX,32.77,96.77",
              "Denver,CO,39.75,105.00"]
westtoeastnames = [
            "Denver",
            "Cheyenne",
            "Dallas",
            "Chicago",
            "Cincinnati",
            "Columbus",
            "Charleston",
            "Cleveland",
            "Columbia",
            "Charlotte",
          ]
cities = [City(s) for s in citystrings]
cities.sort()
sortednames = [c.name() for c in cities]
print(sortednames)
print(westtoeastnames)
['Cheyenne', 'Denver', 'Charlotte', 'Columbia', 'Cleveland', 'Charleston', 'Columbus', 'Cincinnati', 'Chicago', 'Dallas']
['Denver', 'Cheyenne', 'Dallas', 'Chicago', 'Cincinnati', 'Columbus', 'Charleston', 'Cleveland', 'Columbia', 'Charlotte']

这段代码试图用它__lt__()来对城市进行排序,以确定它们在西边的距离以及经度位于本初子午线以西的经度.我__lt__()在类中编写了一个方法,但citystrings不会排序到正确的顺序.

Answer 1

您将经度和纬度比较为字符串,而不是数字.因此,它们按字典顺序进行比较,而不是数字进行比较,因此'104'将在 之前进行排序,'80'因为'1'它出现'8'在ASCII表之前(跟随其他字符无关紧要).

将值转换为浮点数:

self._latitude = float(self._string[2])
self._longitude = float(self._string[3])

你的比较有一个小错误; 如果经度和纬度都匹配,则返回None而不是False.您可能希望测试相等性并应用@functools.total_ordering()装饰器而不是假设仅__lt__()调用它.

稍微清理代码(并删除name()和location()方法,只使用name和location属性):

from functools import total_ordering

@total_ordering
class City:
    def __init__(self, string):
        self.name, self.state, lat, long = string.split(',')
        self.location = (self._latitude, self._longitude) = float(lat), float(long)

    def __lt__(self, other):
        if not isinstance(other, City):
            return NotImplemented
        # tuples defer ordering to the contents; compare them
        # in (longitude, latitude) order so that if longitude is 
        # equal, the outcome is based on latitude.
        return self.location[::-1] < other.location[::-1]

    def __eq__(self, other):
        if not isinstance(other, City):
            return NotImplemented
        return self.location == other.location

注意,__lt__()真的只需要比较self.location; 元组排序负责其余的事情:

sortednames = [c.name for c in sorted(map(City, citystrings), reverse=True)]

注意reverse=True; 你希望首先列出较大的值(格林威治西部).