如何解决 python 中的 KeyError？ 检查下面的代码

Question

def myFUNC (e):
  return e["Points"]

team_stats = [
            {"76ers" : {"Wins" : 22,
                       "Losses" : 12,
                       "Points" : 647},
            "Nets" :  {"Wins" : 22,
                       "Losses" : 13,
                       "Points" : 629},
            "Bucks" :  {"Wins" : 21,
                       "Losses" : 13,
                       "Points" : 618}}
              ]
print(team_stats.sort(key=myFUNC))

KeyError: 'Points'

Answer 1

The reason you get KeyError is because you trying to access the key "Points" from the outer level of the dictionary, where it does not belong, and even if it did, with the current structure, you will see no difference in the result.

You have a single dict inside a list , there is nothing to sort . If you want to sort the dict , that is only possible if you are using 3.7+ , because from 3.7 onwards, dict s in Python are guaranteed to maintain order . If you do meet the version requirement, then use:

def myFUNC (e):
  return e[1]["Points"]

team_stats = [
            {"76ers" : {"Wins" : 22,
                       "Losses" : 12,
                       "Points" : 647},
            "Nets" :  {"Wins" : 22,
                       "Losses" : 13,
                       "Points" : 629},
            "Bucks" :  {"Wins" : 21,
                       "Losses" : 13,
                       "Points" : 618}}
              ]
result = [dict(sorted(team_stats[0].items(), key=myFUNC))]
print(result)

Which gives

[{'Bucks': {'Wins': 21, 'Losses': 13, 'Points': 618},
  'Nets': {'Wins': 22, 'Losses': 13, 'Points': 629},
  '76ers': {'Wins': 22, 'Losses': 12, 'Points': 647}}]

If you do not meet the version requirement, you need to use an collections.OrderedDict :

from collections import OrderedDict
# replace the `result` line with this:
result = [OrderedDict(sorted(team_stats[0].items(), key=myFUNC))]

Which gives:

[OrderedDict([('Bucks', {'Wins': 21, 'Losses': 13, 'Points': 618}),
              ('Nets', {'Wins': 22, 'Losses': 13, 'Points': 629}),
              ('76ers', {'Wins': 22, 'Losses': 12, 'Points': 647})])]

But I don't see why you need the list here.

Also, list().sort() modifies the list in-place, which not only is useless here, printing this will return None .

Answer 2

I think what you meant is this maybe?

def myFUNC (i):
  return i[1]["Points"]

team_stats =  {"76ers" : {"Wins" : 22,
                       "Losses" : 12,
                       "Points" : 647},
            "Nets" :  {"Wins" : 22,
                       "Losses" : 13,
                       "Points" : 629},
            "Bucks" :  {"Wins" : 21,
                       "Losses" : 13,
                       "Points" : 618}}

print(sorted(team_stats.items(), key=myFUNC))

You sort each name by the points.

Answer 3

The problem is that you have a dictionary inside of list, so when you try to sort the list, it is looking at the outer dictionary, and not the inner ones.

A solution is to use just the dictionary items as follows:

team_stats =     {"76ers" : {"Wins" : 22,
                       "Losses" : 12,
                       "Points" : 647},
            "Nets" :  {"Wins" : 22,
                       "Losses" : 13,
                       "Points" : 629},
            "Bucks" :  {"Wins" : 21,
                       "Losses" : 13,
                       "Points" : 618}}
sorted_teams = list(team_stats.items())  
sorted_teams.sort(key = lambda team : team[1]["Points"])   
# [('Bucks', {'Wins': 21, 'Losses': 13, 'Points': 618}), ('Nets', {'Wins': 22, 'Losses': 13, 'Points': 629}), ('76ers', {'Wins': 22, 'Losses': 12, 'Points': 647})]

Answer 4

If you store your dict outside of a list, you can sort it quite simply.

You can also keep your output as a dict by enclosing the sorted() method in dict()

team_stats =  {"76ers" : {"Wins" : 22,
                   "Losses" : 12,
                   "Points" : 647},
        "Nets" :  {"Wins" : 22,
                   "Losses" : 13,
                   "Points" : 629},
        "Bucks" :  {"Wins" : 21,
                   "Losses" : 13,
                   "Points" : 618}}

dict(sorted(team_stats.items(), key=lambda x: x[1]['Points']))

#{'Bucks': {'Wins': 21, 'Losses': 13, 'Points': 618}, 'Nets': {'Wins': 22, 'Losses': 13, 'Points': 629}, '76ers': {'Wins': 22, 'Losses': 12, 'Points': 647}}

# in reverse
dict(sorted(team_stats.items(), key=lambda x: x[1]['Points'], reverse=True))
#{'76ers': {'Wins': 22, 'Losses': 12, 'Points': 647}, 'Nets': {'Wins': 22, 'Losses': 13, 'Points': 629}, 'Bucks': {'Wins': 21, 'Losses': 13, 'Points': 618}}