Write JSON data to a file in Python

David Y.

The Problem

How can I write a dictionary to a JSON file using Python?

The Solution

We can do this using Python’s built-in json library and file operations. Specifically, the json.dump function allows us to serialize a Python dictionary as JSON for writing to disk. For example:

import json data = {"firstname": "John", "lastname": "Doe", "age": 35} with open("data.json", "w") as f: json.dump(data, f, indent=4)

The indent keyword argument specifies the number of spaces to use for indentation when formatting the JSON data.

Note that if our dictionary contains any keys that are not strings, integers, floats, booleans, or None, this code will raise a TypeError. To skip these keys instead, we can pass skip_keys=True to json.dump.

If we would like to sort the JSON object’s keys before writing it to our file, we can pass sort_keys=True to the function.

To load JSON data from a file into a dictionary, we can use json.load:

with open("data.json", "r") as f: data = json.load(f) # will be { "firstname": "John", "lastname": "Doe", "age": 35 }

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