无法更新嵌套字典中的单个值

Question

在创建像 {'key': {'key': {'key': 'value'}}} 这样的字典后，我运行遇到了尝试为更高深度键设置值的问题。更新其中一个值后，（其他键的）剩余值的值也被更新。

这是我的 Python 代码：

times = ["09:00", "09:30", "10:00", "10:30"]
courts = ["1", "2"]

daytime_dict = dict.fromkeys(times)
i = 0
for time in times:
    daytime_dict[times[i]] = dict.fromkeys(["username"])
    i += 1

courts_dict = dict.fromkeys(courts)
k = 0
for court in courts:
    courts_dict[courts[k]] = daytime_dict
    k += 1

day_info = [('name', '09:00', 1), ('name', '09:30', 1)]
for info in day_info:
    info_court = str(info[2])
    time = info[1]
    # Here I am trying to set the value for courts_dict['1']['09:00']["username"] to be 'name', 
    # but the value for courts_dict['2']['09:00']["username"] and courts_dict['3']['09:00']["username"] is also set to 'name'
    # What am I doing wrong? How can I only update the value for where the court is '1'?
    courts_dict[info_court][time]["username"] = info[0]

我想得到这个：

{'1': {'09:00': {'username': 'name'},
       '09:30': {'username': 'name'},
       '10:00': {'username': None},
       '10:30': {'username': None}},
 '2': {'09:00': {'username': None},
       '09:30': {'username': None},
       '10:00': {'username': None},
       '10:30': {'username': None}}

但我明白了：

{'1': {'09:00': {'username': 'name'},
       '09:30': {'username': 'name'},
       '10:00': {'username': None},
       '10:30': {'username': None}},
 '2': {'09:00': {'username': 'name'},
       '09:30': {'username': 'name'},
       '10:00': {'username': None},
       '10:30': {'username': None}}

（看看 court_dict['2']['09:00']['username'] 和 court_dict['2']['09:30']['username'] 是如何同时更新的，而我只想更新来自 court_dict['1'] 的值）

从逻辑上讲，我无法理解为什么在更新 courts_dict 时会更新两个值（我在最后一行代码中的做法），而不是只更新一个。由于 info_court 是 "1"，我认为只有那个法院的 "username" 会被更新。

我做错了什么？

Answer 1

Logically, I can't understand why both values are updated when I update the courts_dict

对于您正在使用的字典对象，您正在分配相同的对象 references 作为值，因此您看到“两个值都已更新”的原因。您可能想使用 copy 或 deepcopy:

重新编写代码

https://docs.python.org/3/library/copy.html

Assignment statements in Python do not copy objects, they create bindings between a target and an object. For collections that are mutable or contain mutable items, a copy is sometimes needed so one can change one copy without changing the other.

无法更新嵌套字典中的单个值

Can't update a single value in a nested dictionary

python

dictionary

data-structures