如何修改字典遍历代码：将关注列表转换为粉丝列表

你当前使用的用户字典如下：

members = {
    1: {"name": "Farly Waller", "country": "Russia", "following": [11, 18, 17, 20]},
    2: {"name": "Jania Hardistry", "country": "Indonesia", "following": [3, 8, 15, 20]},
    3: {"name": "Yale Shortan", "country": "Brazil", "following": [2, 4, 8]},
    4: {"name": "Redford Melloi", "country": "Philippines", "following": [1, 3, 13, 14]},
    5: {"name": "Lisbeth Cello", "country": "Pakistan", "following": [4, 7, 10]},
    6: {"name": "Andrew Flaonier", "country": "Pakistan", "following": []},
    7: {"name": "Pris Pilmore", "country": "Japan", "following": [5, 6, 9, 1, 15, 16]},
    8: {"name": "Starla Buffey", "country": "Colombia", "following": [10, 2, 3]},
    9: {"name": "Clark Goymer", "country": "Thailand", "following": [7, 11]},
    10: {"name": "Gayle Testin", "country": "Brazil", "following": [8, 5, 15, 19, 13]},
    11: {"name": "Serena Brombell", "country": "China", "following": [1, 17, 18]},
    12: {"name": "Wendy Toke", "country": "Peru", "following": []},
    13: {"name": "Clarice Shelmardine", "country": "Portugal", "following": [10, 1, 14, 15, 16, 19]},
    14: {"name": "Julie Corradeschi", "country": "Peru", "following": [13, 1, 2, 4]},
    15: {"name": "Constantin Sebire", "country": "China", "following": [3, 10, 13, 16, 18]},
    16: {"name": "Annadiane Mum", "country": "Japan", "following": [7, 13, 6, 18]},
    17: {"name": "Lovell Lubbock", "country": "China", "following": [1, 11, 20]},
    18: {"name": "Gwynne Toplis", "country": "China", "following": [1, 11, 16, 17]},
    19: {"name": "Pammy Urey", "country": "Yemen", "following": [10, 6, 13, 20]},
    20: {"name": "Celestina Phillipps", "country": "Canada", "following": [3, 17]},
}

你写的代码如下：

followers = {}
for user_id in members:
    followers[user_id]=[]
    for user1 in members[user_id]["following"]:
        if user1 in members[user_id]["following"]: 
            followers[user_id].append(user1)
print(followers)

这段代码只是把每个用户的关注列表直接复制到followers字典中，但你实际需要的是每个用户的粉丝列表——也就是哪些用户关注了当前用户。比如用户5的粉丝列表应为[7, 10]，用户1的粉丝列表应为[4, 7, 11, 13, 14, 17, 18]。

修改代码的核心逻辑是：遍历每个用户的关注列表，将当前用户ID添加到他所关注的用户的粉丝列表中。具体代码如下：

# 初始化所有用户的粉丝列表为空
followers = {user_id: [] for user_id in members}

# 遍历每个用户及其数据
for current_user_id, user_info in members.items():
    # 遍历当前用户关注的每一个用户
    for followed_id in user_info["following"]:
        # 将当前用户添加到被关注用户的粉丝列表里
        followers[followed_id].append(current_user_id)

print(followers)

逻辑说明： #

1. 初始化粉丝字典：用字典推导式快速创建一个包含所有用户ID的字典，每个ID对应一个空列表，确保没有用户被遗漏。
2. 遍历用户与关注列表：外层循环逐个取出用户ID和对应的信息，内层循环遍历该用户关注的所有ID。
3. 填充粉丝列表：每遍历到一个被关注的ID，就把当前用户ID添加到这个被关注ID的粉丝列表中——这就相当于记录了“当前用户关注了这个ID，所以当前用户是这个ID的粉丝”。

运行这段代码后，就能得到你需要的粉丝列表：

• 用户5的粉丝列表为[7, 10]（用户7和10都关注了5）
• 用户1的粉丝列表为[4, 7, 11, 13, 14, 17, 18]，完全符合预期。

内容的提问来源于stack exchange，提问作者Emma__BB