Using JSON in Python

JSON (JavaScript Object Notation) is a human-readable data interchange format that is supported by most programming languages. Python has built-in support for JSON via the json module.¹ This module can be used to encode and decode JSON data (serialize and deserialize).

Importing

To use the json module, you need to import it:

import json

Basic Encoding and Decoding

There are two basic ways for encoding and decoding JSON data. You can either encode to string or to a file directly.

Using Strings

Encoding a JSON string from a Python object can be done with the json.dumps() (dump to string) function.

# A simple Python object (dictionary)
python_object = {
    "name": "John",
    "age": 30,
    "city": "Auckland"
}

# Encode the Python object to a JSON string
json_string = json.dumps(python_object)

print(json_string)
# The JSON string will be:
# {"name": "John", "age": 30, "city": "Auckland"}

To decode a JSON string to a Python object (i.e. go the other way), use the json.loads() (load from string) function.

# A JSON string
json_string = '{"name": "John", "age": 30, "city": "Auckland"}'

# Decode the JSON string to a Python object (this will end up as a dictionary)
python_object = json.loads(json_string)

print(python_object)
# The Python object will be:
# {'name': 'John', 'age': 30, 'city': 'Auckland'}

Using File Objects

To encode a Python object to a JSON string and save it to a file, use the json.dump() (note there is no ‘s’ at the end of the function name) function, passing in a file object that is writeable. A common way to create a file object is to open a file in write mode with the with statement.

# A Python object
python_object = {
    "name": "John",
    "age": 30,
    "city": "Auckland"
}

# Open a file for writing
with open('data.json', 'w') as file:
    # Write the Python object to the file
    json.dump(python_object, file)

Compact Encoding

Compact encoding can be done by passing separators=(',', ':') to the json.dumps() function.

json_string = json.dumps(python_object, separators=(',', ':'))

print(json_string)
# The JSON string will be (note the lack of spaces):
# {"name":"John","age":30,"city":"Auckland"}

Footnotes

1. Python.org. 3.13.2 Documentation » The Python Standard Library » Internet Data Handling » json — JSON encoder and decoder [documentation]. Retrieved 2025-03-12, https://docs.python.org/3/library/json.html. ↩