Python 设置嵌套字典中键相同时的键值

Question

Really simple situation but I can't seem to find the answer anywhere. I have a dictionary that contains a bunch of other dictionaries that I'm using to store configurations. Each nested dictionary is created from the same template, so the keys are the same. When trying to set a key in one of them, the same key across all the nested dictionaries gets updated with the value.

Here's an example of the kind of thing I'm doing.

my_dict = {
    "bar": {
        "baz": None,
        "qux": None
    },
    "foo": {
        "baz": None,
        "qux": None
    }
}

my_dict['foo']['baz'] = True

Then the dictionary looks like this, I don't understand why? I'm sure I've done this kind of thing fine before as well which is why its confusing.

{
    "bar": {
        "baz": True,
        "qux": None
    },
    "foo": {
        "baz": True,
        "qux": None
    }
}

EDIT

The nested dictionaries are created using a template like this:

temp = {'baz': None,
        'qux': None}
 
my_dict['foo'] = temp
my_dict['bar'] = temp

Any help would be greatly appreciated, Thank You

Answer 1

You need to use the copy method in order to copt a dict type without them being related to each others:

my_dict = {}

temp = {'baz': None,
        'qux': None}
 
my_dict['foo'] = temp.copy()
my_dict['bar'] = temp.copy()

print(my_dict)
my_dict['foo']['baz'] = True
print(my_dict)

Output:

{'bar': {'baz': None, 'qux': None},
 'foo': {'baz': None, 'qux': None}}

{'bar': {'baz': None, 'qux': None},
 'foo': {'baz': True, 'qux': None}}

Note: You don't need to call .copy() twice in this case, because you're not using temp elsewhere in your code. So it changing it's content is fine as long as you have another dict that does use .copy() .

Answer 2

Your problem occurs because you're pointing my_dict['foo'] and my_dict['bar'] to the same object. So once that object is changed, the value for both will be changed.

On top of what Ann has, you could try using this since your dictionary is shallow:

my_dict = {}

temp = {'baz': None,
        'qux': None}
 
my_dict['foo'] = dict(temp)
my_dict['bar'] = dict(temp)

print(my_dict)
my_dict['foo']['baz'] = True
print(my_dict)

dict creates a new dictionary object.