的Python：迭代给定的嵌套字典

Question

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，我可以在这样的结构中提取的键和值：

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 

但我有点困惑如何访问所有playlists names for playlists和所有artists for tracks in playlists使用任何iteration工具。

我该怎么办？

Answer 1

您可以使用下面的代码来访问播放列表的名称和艺术家名称：

# 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'] 

注意，上面的Python 2只工作，与Python 3 values & keys应代替itervalues & iterkeys。

Answer 2

如果您想要提取所有播放列表名称的平面列表，您可以使用列表理解。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'] 

注意，这将会给整个的播放列表字典