Updating a single value in a nested JSON file using a list of strings as keys

Question

I have a JSON file, for example:

{
    "items": {
        "item1": {
            "thing1": "SomeValue", 
            "thing2": "AnotherValue"
        }, 
        "item2": {
            "thing1": "SomeValue", 
            "thing2": "AnotherValue"
        },
        "item3": {
            "thing1": {
                "moreStuff": "someStuff",
                "evenMoreStuff": "someMoreStuff"
            }
        }
    }
}

I want to make a generic function to update a single value in the file by passing a list of strings as keys.

def update_dict(value, keys):
    with open(somePath, "r") as f:
        data = json.load(f)
    
    data[keys[0]][keys[1]][keys[2]] = value

    with open(somePath, "w") as f:
        json.dump(data, f,

value = "AThirdValue"
keys = ["items", "item2", "thing1"]

update_dict(value, keys)

What I can't figure out is how this can be done if one does not know the length of the keys list. For example this would not work:

value = "AThirdValue"
keys = ["items", "item3", "thing1", "moreStuff"]
update_dict(value, keys)

I would not want to use if-statements to check the length and then having to edit this function if I add another level of depth.

iBug · Accepted Answer · 2021-03-11 19:33:33Z

1

You can use a loop to simulate tree-walking:

def update_dict(value, keys):
    with open(somePath, "r") as f:
        data = json.load(f)

    point = data
    last_key = keys.pop()
    for key in keys:
        point = point[key]
    
    point[last_key] = value

    with open(somePath, "w") as f:
        json.dump(data, f)

answered Mar 11, 2021 at 19:33

iBug

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Comments

mahmed nabil · Accepted Answer · 2021-03-11 20:02:33Z

you could cascade the items of the keys list like these

import json

def update_dict(value, keys):
    with open(somePath, "r") as f:
        data = json.load(f)
    
    tmp_data = data
    for key in keys[:-1]:
        tmp_data = tmp_data[key]
    tmp_data[keys[-1]] = value 
    with open(somePath, "w") as f:
        json.dump(data, f)

value = "AThirdValue"
keys = ["items", "item2", "thing1"]

update_dict(value, keys)

other way to code it

import json

def update_dict(value, *keys):
    with open(somePath, "r") as f:
        data = json.load(f)
    
    tmp_data = data
    for key in keys[:-1]:
        tmp_data = tmp_data[key]
    tmp_data
    tmp_data[keys[-1]] = value 
    with open(somePath, "w") as f:
        json.dump(data, f)

value = "AThirdValue"
update_dict(value, "items", "item2", "thing1")

curiouscurl · Accepted Answer · 2021-03-11 19:49:11Z

0

Use variable number of arguments.

def functionName(*argument)

Replace:

data[keys[0]][keys[1]][keys[2]] = value

with:

def update_dict(value, *keys):
    with open(somePath, "r") as f:
        data = json.load(f)

    # data[keys[0]][keys[1]][keys[2]] = value
    for key in keys:
        data[key] = value

    with open(somePath, "w") as f:
        json.dump(data, f)

value="AThirdValue"
keys = ["items", "item2", "thing1"]

update_dict(value, keys)

answered Mar 11, 2021 at 19:49

curiouscurl

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