How to update a JSON file by using Python?

Question

I am using Python and I have a JSON file in which I would like to update a value related to a given key. That is, I have the my_file.json containing the following data

{"a": "1", "b": "2", "c": "3"}

and I would like to just change the value related to the b key from 2 to 9 so that the updated file look as like:

{"a": "1", "b": "9", "c": "3"}

How can I make that?

I tried the following but without success (the changes are not saved to the file):

with open('my_file.json', 'r+') as f:
    json_data = json.load(f)
    json_data['b'] = "9"
    f.close()

This may help : stackoverflow.com/questions/21035762/…

Vipul
– Vipul

2014-07-04 19:28:42 +00:00
Commented Jul 4, 2014 at 19:28 — Vipul
– Vipul, Commented Jul 4, 2014 at 19:28

Gino Mempin · Accepted Answer · 2020-07-29 12:58:34Z

15

You did not save the changed data at all. You have to first load, then modify, and only then save. It is not possible to modify JSON files in-place.

with open('my_file.json', 'r') as f:
    json_data = json.load(f)
    json_data['b'] = "9"

with open('my_file.json', 'w') as f:
    f.write(json.dumps(json_data))

You may also do this:

with open('my_file.json', 'r+') as f:
    json_data = json.load(f)
    json_data['b'] = "9"
    f.seek(0)
    f.write(json.dumps(json_data))
    f.truncate()

If you want to make it safe, you first write the new data into a temporary file in the same folder, and then rename the temporary file onto the original file. That way you will not lose any data even if something happens in between.

If you come to think of that, JSON data is very difficult to change in-place, as the data length is not fixed, and the changes may be quite significant.

edited Jul 29, 2020 at 12:58

Gino Mempin

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answered Jul 4, 2014 at 19:25

DrV

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2 Comments

user502052 Over a year ago

Can you provide a concrete example?

Zion Oyemade Over a year ago

There is a missing colon : on line 5 - first code category with open('my_file.json', 'w') as f:

timgeb · Accepted Answer · 2014-07-04 19:32:16Z

2

You are almost there, you only have to write the updated json_data back to the file. Get rid of f.close(), as the with statement will ensure that the file is closed. Then, issue

with open('my_file.json', 'w') as f:
    f.write(json.dumps(json_data))

edited Jul 4, 2014 at 19:32

answered Jul 4, 2014 at 19:26

timgeb

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2 Comments

timgeb Over a year ago

@DrV point taken, another with block is probably cleaner than seek(0)

DrV Over a year ago

@timgeb: seek is also a nice solution, see my answer.

Suhas Jadhav · Accepted Answer · 2016-12-29 01:18:11Z

1

This is simplest way to do the json file updation/writing. where you are creating instance of json file as 'f' and the writing the 'data' into the json file,

#write json file

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

#Read json file

with open('data.json', 'r') as f:
    json.load(data, f)

answered Dec 29, 2016 at 1:18

Suhas Jadhav

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Comments

Gabriel Braico Dornas · Accepted Answer · 2021-10-27 15:22:04Z

0

Open the file and store in one variable all the content using json.load function
Update your key stored in the previous variable
Open the file another time and update your content with the variable updated

def updateJsonFile():
    jsonFile = open("my_file.json", "r") # Open the JSON file for reading
    data = json.load(jsonFile) # Read the JSON into the buffer
    jsonFile.close() # Close the JSON file

    ## Working with buffered content
    data["b"] = "9"

    ## Save our changes to JSON file
    jsonFile = open("my_file.json", "w+")
    jsonFile.write(json.dump(data))
    jsonFile.close()

edited Oct 27, 2021 at 15:22

answered Oct 25, 2021 at 20:48

Gabriel Braico Dornas

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1 Comment

Sylvester is on codidact.com Over a year ago

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