JSON (JavaScript Object Notation) is a standard text format for storing and transporting data. It is highly common when data is sent from a server to a web page or between APIs.

Python has a built-in package called json, which can be used to work with JSON data.

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1. JSON format

JSON looks exactly like a Python dictionary as a string.

{
  "name": "John",
  "age": 30,
  "city": "New York"
}

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2. json.loads() (JSON to Python)

If you have a JSON string, you can parse it by using the json.loads() method. The result will be a Python dictionary.

import json

# some JSON string:
x = '{"name":"John", "age":30, "city":"New York"}'

# parse x:
y = json.loads(x)

# the result is a Python dictionary:
print(y["age"]) # 30

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3. json.dumps() (Python to JSON)

If you have a Python object, you can convert it into a JSON string by using the json.dumps() method.

import json

# a Python object (dict):
x = {
  "name": "John",
  "age": 30,
  "city": "New York"
}

# convert into JSON:
y = json.dumps(x)

# the result is a JSON string:
print(y)

Formatting the Output

The json.dumps() method has parameters to make it easier to read the result.

• indent: defines the numbers of indents
• separators: changes the default separator
• sort_keys: specifies if the result should be sorted or not

print(json.dumps(x, indent=4, sort_keys=True))

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4. Parse JSON from file (load(), dump())

If you are working with files instead of strings, you use load() and dump() (without the ‘s’).

json.load() (File to Python)

Reads a JSON file and parses it into a Python object.

import json

with open("data.json", "r") as file:
    data = json.load(file)
    print(data)

json.dump() (Python to File)

Writes a Python object to a file in JSON format.

import json

data = {"name": "Alice", "role": "Admin"}

with open("output.json", "w") as file:
    json.dump(data, file, indent=4)

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5. Convert custom objects to JSON

The json module only understands standard primitive types (dicts, lists, strings, ints, floats, booleans, None).

If you try to serialize a custom class object, it will throw a TypeError.

To convert custom objects, you must write a custom encoder, or define a method inside your class that returns a serializable dictionary format.

import json

class User:
    def __init__(self, name, age):
        self.name = name
        self.age = age

user = User("Bob", 25)

# Convert the object's __dict__ attribute which is a dictionary of its properties
json_string = json.dumps(user.__dict__)

print(json_string) # {"name": "Bob", "age": 25}