design twitter leetcode大神求帮助

最近看了这个leetcode题 然后有个人post 一个答案

1. class Twitter(object):
   
2. 
   
3.     def __init__(self):
   
4.         """
   
5.         Initialize your data structure here.
   
6.         """
   
7.         self.tweets = collections.defaultdict(list)
   
8.         self.following = collections.defaultdict(set)
   
9.         self.order = 0
   
10.         
    
11. 
    
12.     def postTweet(self, userId, tweetId):
    
13.         """
    
14.         Compose a new tweet.
    
15.         :type userId: int
    
16.         :type tweetId: int
    
17.         :rtype: None
    
18.         """
    
19.         self.tweets[userId] += (self.order, tweetId),
    
20.         self.order -= 1
    
21. 
    
22.     def getNewsFeed(self, userId):
    
23.         """
    
24.         Retrieve the 10 most recent tweet ids in the user's news feed. Each item in the news feed must be posted by users who the user followed or by the user herself. Tweets must be ordered from most recent to least recent.
    
25.         :type userId: int
    
26.         :rtype: List[int]
    
27.         """
    
28. 
    
29.         tw = sorted(tw for i in self.following[userId] | {userId} for tw in self.tweets[i])[:10]
    
30.         
    
31.         print(tw)
    
32.         return [news for i, news in tw]
    
33.         
    
34.     def follow(self, followerId, followeeId):
    
35.         """
    
36.         Follower follows a followee. If the operation is invalid, it should be a no-op.
    
37.         :type followerId: int
    
38.         :type followeeId: int
    
39.         :rtype: None
    
40.         """
    
41.         self.following[followerId].add(followeeId)
    
42.         
    
43. 
    
44.     def unfollow(self, followerId, followeeId):
    
45.         """
    
46.         Follower unfollows a followee. If the operation is invalid, it should be a no-op.
    
47.         :type followerId: int
    
48.         :type followeeId: int
    
49.         :rtype: None
    
50.         """
    
51.         self.following[followerId].discard(followeeId)
    

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请问 tw = sorted(tw for i in self.following[userId] | {userId} for tw in self.tweets[i])[:10] 这行是怎么回事 谢谢！！！

翻译：

1. twitters = []
   
2. for i in self.following[userId] | {userId}:
   
3.     for tw in self.tweets[i]:
   
4.         twitters += tw
   
5. return sorted(twitters)[:10]

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