trying to access nested dictionary keys in python

Question

I need to load a json and read the content to edit it later. I am getting

{TypeError}string indices must be integers

here is the json structure (note-below is the format when json file is already loaded, else it shows double quotes)

data ={'a':'hello','b':'{"date1":"9/21/2021","date2":"9/22/2021"}','c':'new'}

when trying to access data['b']['date1'] it throws error

code is as follows

jsonfile=open(file.json, "r")
data = json.load(jsonfile)
jsonfile.close()
date = data['b']['date1']

Because 'b'’s key is a string, not a dict. You can use the ast.literal_eval function or json library to convert the string into a dict. — s3dev
– s3dev, Commented Sep 21, 2021 at 16:55
I want to read date1 and date2 and need to update those in the json file but while trying to access date1, I get the mentioned error. How can I access those keys that are inside b ? — viki
– viki, Commented Sep 21, 2021 at 16:58
can anyone tell if its not a nested dictionary then what kind of structure it is ? — viki
– viki, Commented Sep 21, 2021 at 18:25

Niel Godfrey P. Ponciano · Accepted Answer · 2021-09-21 17:34:17Z

2

The content of data['b'] is a string which contains a JSON document:

'{"date1":"9/21/2021","date2":"9/22/2021"}'

Thus you should convert it first to JSON (dict / list):

data_b = json.loads(data['b'])

Now that it is converted to a dict, you can already access its keys:

data_b["date1"]

If you want to update those values, then update the dict and then convert it back to string and reassign to the original data:

import json

data = {'a':'hello','b':'{"date1":"9/21/2021","date2":"9/22/2021"}','c':'new'}

data_b = json.loads(data['b'])
data_b["date1"] = "updated 1"
data_b["date2"] = "updated 2"

data['b'] = json.dumps(data_b)
print(data)

Output:

{'a': 'hello', 'b': '{"date1": "updated 1", "date2": "updated 2"}', 'c': 'new'}

To write it back, you have to open the file in write-mode w and then use either json.dump() or file.write().

with open("file.json", 'w') as json_file:
    # Option 1
    json.dump(data, json_file)
    # Option 2
    # json_file.write(json.dumps(data))

edited Sep 21, 2021 at 17:34

answered Sep 21, 2021 at 16:58

Niel Godfrey P. Ponciano

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7 Comments

viki Over a year ago

thanks for the details Niel. I still have a little confusion when writing it back to the file: jsonfile=open(file.json, "r") data = json.load(jsonfile) date_1 = json.loads(data['b']) jsonfile.close() data_1["date1"] = "updated 1" data_1["date2"] = "updated 2" jsonfile = open("file.json", "w+") jsonfile.write(json.dumps(data_1)) jsonfile.close() how to handle that in file, its replacing the file with only b's content

Niel Godfrey P. Ponciano Over a year ago

@viki It is because you are only dumping data_1 which only contains the contents for b. What you need is the whole data. I updated my answer to include how the updated json must be updated. Could you check if it works on your side?

viki Over a year ago

I tried data and data_1 while dumping. The json file doesn't get any update when using data, but it gets updated and provide me only b value when using data_1. Not sure why. I have provide the code on the above comment, not sure how to format it like you are doing for proper reading

viki Over a year ago

the update that we are making on data_1 is not getting into data. So the json file stays the same. not sure how to handle it

viki Over a year ago

I found my mistake, I was missing one step data['b'] = json.dumps(data_b). I think I got this working with you help. Thanks a lot. Appreciate timely help

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