Python嵌套字典排序问题：按points排序未达预期结果求助

问题描述 #

我想要根据points对嵌套字典中的球队进行排序，编写了排序代码但未得到预期效果。期望排序顺序为Spain、Portugal、Morocco、Iran。

原始字典 #

{
    'Spain': {
        'wins': 3,
        'loses': 0,
        'draws': 0,
        'goal difference': 4,
        'points': 9
    },
    'Iran': {
        'wins': 0,
        'loses': 3,
        'draws': 0,
        'goal difference': -6,
        'points': 0
    },
    'Portugal': {
        'wins': 2,
        'loses': 1,
        'draws': 0,
        'goal difference': 4,
        'points': 6
    },
    'Morocco': {
        'wins': 1,
        'loses': 2,
        'draws': 0,
        'goal difference': -2,
        'points': 3
    }
}

使用的排序代码 #

from collections import OrderedDict

sorted_dict = OrderedDict(sorted(B_group.items(), key=lambda x: x[1]["points"], reverse=True))

当前得到的结果 #

Spain  wins:3 , loses:0 , draws:0 , goal difference:4 , points:9
Iran  wins:0 , loses:3 , draws:0 , goal difference:-6 , points:0
Portugal  wins:2 , loses:1 , draws:0 , goal difference:4 , points:6
Morocco  wins:1 , loses:2 , draws:0 , goal difference:-2 , points:3

问题分析与解决方案 #

你的排序代码逻辑本身是正确的，当前结果顺序异常大概率是输出方式错误——比如你可能没遍历排序后的OrderedDict，而是直接输出了原字典，或者输出代码存在疏漏。

验证排序是否生效的正确方式是遍历排序后的结果：

for team, stats in sorted_dict.items():
    print(f"{team}  wins:{stats['wins']} , loses:{stats['loses']} , draws:{stats['draws']} , goal difference:{stats['goal difference']} , points:{stats['points']}")

执行这段代码后，会得到你期望的顺序：

Spain  wins:3 , loses:0 , draws:0 , goal difference:4 , points:9
Portugal  wins:2 , loses:1 , draws:0 , goal difference:4 , points:6
Morocco  wins:1 , loses:2 , draws:0 , goal difference:-2 , points:3
Iran  wins:0 , loses:3 , draws:0 , goal difference:-6 , points:0

另外，在Python 3.7+版本中，普通字典默认保持插入顺序，也可以不用OrderedDict，直接生成排序后的列表处理：

sorted_teams = sorted(B_group.items(), key=lambda x: x[1]["points"], reverse=True)
for team, stats in sorted_teams:
    print(f"{team}  wins:{stats['wins']} , loses:{stats['loses']} , draws:{stats['draws']} , goal difference:{stats['goal difference']} , points:{stats['points']}")

内容的提问来源于stack exchange，提问作者yosef