Python：迭代嵌套字典

Question

给出以下dictionary ：

playlists={'user':[
               {'playlist1':{
                    'tracks': [        
                    {'name': 'Karma Police','artist': 'Radiohead', 'count': "1.0"},
                    {'name': 'Bitter Sweet Symphony','artist': 'The Verve','count': "2.0"}                    
                     ]
                    }
               },
               {'playlist2':{
                    'tracks': [        
                    {'name': 'We Will Rock You','artist': 'Queen', 'count': "3.0"},
                    {'name': 'Roxanne','artist': 'Police','count': "5.0"}                    
                     ]
                  }
                },
              ]
            }

虽然不是很优雅，但我可以在这样的结构中获取键和值：

keys ：

userX = [user[0] for user in playlists.iteritems()][0] //userX
playlist1 = list(playlists['userX'][0].keys())[0] //playlist1

和嵌套values ：

artist = playlists['user'][0]["playlist1"]['tracks'][0]['artist'] //Radiohead
count = playlists['user'][1]["playlist2"]['tracks'][0]['count'] //3.0

但是我对使用任何iteration工具如何访问playlists names for playlists和所有artists for tracks in playlists所有playlists names for playlists感到困惑。

我该怎么做？

Answer 1

您可以使用以下代码访问播放列表名称和艺术家姓名：

# Define generator to return dicts under each user
lists = (x for user in playlists.itervalues() for x in user)
print [name for play_list in lists for name in play_list.iterkeys()]

lists = (x for user in playlists.itervalues() for x in user)
track_lists = (content['tracks'] for p in lists for content in p.itervalues())
print [track['artist'] for track_list in track_lists for track in track_list]

输出：

['playlist1', 'playlist2']
['Radiohead', 'The Verve', 'Queen', 'Police']

请注意，上面只适用于Python 2，应使用Python 3 values和keys而不是itervalues和iterkeys 。

Answer 2

如果您要提取所有播放列表名称的平面列表，可以使用列表推导。 字典和列表的混合增加了一点复杂性。

all_playlists = [ playlist_title 
                  for user in playlists 
                  for user_playlists in playlists[user]
                  for playlist_title in user_playlists ]
print all_playlists

all_artists = [ track['artist']
                for user in playlists
                for user_playlists in playlists[user]
                for playlist_title in user_playlists 
                for track in user_playlists[playlist_title]['tracks'] ]
print all_artists

给

['playlist1', 'playlist2']
['Radiohead', 'The Verve', 'Queen', 'Police']

请注意，这将为播放列表中的所有用户提供播放列表/艺术家的组合列表