Table of Contents
2. Modify the data structure according to requirements
3. Write the modified content back to the file
Home Backend Development Python Tutorial How to update a JSON file in Python?

How to update a JSON file in Python?

Jul 16, 2025 am 03:49 AM
python JSON files

Updating a JSON file requires three steps: reading, modifying, and writing. 1. Use json.load() to read the file into a Python data structure; 2. Access the modified value through keys such as data['age']=31 or nested modification; 3. Use json.dump(data,f) to save the changes back to the file and it is recommended to add indent to beautify the output. Before operation, you should confirm that the file exists and backups should be made if necessary. Remote data must be processed in conjunction with the requests module.

How to update a JSON file in Python?

Updating a JSON file is actually quite straightforward in Python. As long as you understand the three steps of reading, modifying, and writing, you will basically master it. Here are some situations and corresponding practices you may encounter.

How to update a JSON file in Python?

1. Read the content of the JSON file first

If you want to modify something, you must first load the data in the file. Python provides built-in json modules to handle this problem.

 import json

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

In this way, you will turn the file content into a Python dictionary or list structure, and you can do various operations on it next.

How to update a JSON file in Python?

2. Modify the data structure according to requirements

This step is the most flexible, depending on what you want to change. For example, you want to add a field, modify a value, or delete an item.

For example, suppose your data.json is like this:

How to update a JSON file in Python?
 {
    "name": "Alice",
    "age": 30
}

If you want to change your age to 31, you can write it like this:

 data['age'] = 31

If you want to add a new field:

 data['city'] = 'Beijing'

If it is a nested structure, for example:

 {
    "user": {
        "name": "Bob",
        "info": {
            "age": 25,
            "email": "bob@example.com"
        }
    }
}

If you want to change your email, you have to go in layer by layer:

 data['user']['info']['email'] = 'new_email@example.com'

In short, as long as the structure is right, it can be changed no matter what.


3. Write the modified content back to the file

Don't forget to save it back after modification. At this time, you are using json.dump() or json.dumps() . It is recommended to use dump to write directly to the file.

 with open('data.json', 'w') as f:
    json.dump(data, f, indent=4)

Adding indent=4 can make the output more beautiful and suitable for debugging or viewing.

Note: If you don't add this parameter, the entire JSON will be compressed into one line. Although the function is OK, it is not good-looking.


4. Other tips

  • If you are not sure whether the file exists, you can use os.path.exists() to make a judgment.
  • It is best to make a backup before modification, especially important data.
  • If it is a remote JSON (such as the API interface returns), it is not a "file" operation, but it must be used with the requests module.
  • If you just want to test temporarily, you can also use strings, such as json.loads() and json.dumps() .

Basically these are the operations. Although it seems simple, sometimes the format is wrong, the path is wrong, or the file is not closed, which can easily lead to problems. As long as you follow the steps, it can usually be done.

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