The full form of JSON is Javascript Object Notation. It means that a script (executable) file which is made of text in a programming language, is used to store and transfer the data. Python supports JSON through a built-in package called JSON. To use this feature, we import the JSON package in Python script. The text in JSON is done through quoted-string which contains the value in key-value mapping within {}. It is similar to the dictionary in Python.

Reading JSON from a file using Python

Reading JSON in Python means retrieving JSON data from a file or string and converting it into Python objects like dictionaries or lists. This process is called deserialization. Python offers two main ways to read JSON data:

1. Using json.load() 

The JSON package has json.load() function that loads the JSON content from a JSON file into a dictionary. It takes one parameter:

File pointer: A file pointer that points to a JSON file.

Example: Read a JSON file and convert its contents to a Python dictionary.

import json

# Read from file and parse JSON
with open("sample.json", "r") as f:
    data = json.load(f)

print(data)
print(type(data))

Output: 

Explanation: We open sample.json in read mode and use json.load() to parse its content into a Python dictionary, which we then print along with its data type.

2. Using json.loads()

json.loads() function is used to parse a JSON string and convert it into a Python object. It takes one parameter:

JSON string: A valid JSON-formatted string.

Example: Convert a JSON-formatted string into a Python dictionary.

import json
json_str = '{"name": "Francis", "age": 25, "city": "New York"}'
data = json.loads(json_str)

print(data)
print(type(data))

Explanation: We define a JSON string and use json.loads() to parse it into a Python dictionary, then print the resulting object and its type.

Writing JSON to a file in Python

Writing data to a JSON file in Python involves converting Python objects like dictionaries into JSON format and saving them to a file. This process is called serialization. Let's explore two methods to write a JSON file in Python.

1. Using json.dumps() 

The JSON package in Python has a function called json.dumps() that helps in converting a dictionary to a JSON object. It takes two parameters:

• dictionary: the name of a dictionary which should be converted to a JSON object.
• indent: defines the number of units for indentation

After converting the dictionary to a JSON object, simply write it to a file using the "write" function.

Example: Convert a dictionary to a JSON string and write it to a file.

import json
data = {
    "name": "sathiyajith",
    "rollno": 56,
    "cgpa": 8.6,
    "phone": "9976770500"
}

json_str = json.dumps(data, indent=4)
with open("sample.json", "w") as f:
    f.write(json_str)

Output: 

Explanation: We create a dictionary, convert it to a JSON-formatted string using json.dumps() with 4-space indentation and write it to sample.json using the write() method.

2. Using json.dump() 

Another way of writing JSON to a file is by using json.dump() method. The JSON package has "dump" function which directly writes the dictionary to a file in the form of JSON, without needing to convert it into an actual JSON object. It takes 2 parameters:

• dictionary - the name of a dictionary which should be converted to a JSON object.
• file pointer - pointer of the file opened in write or append mode.

Example: Directly write a dictionary to a JSON file without converting it first.

import json
data = {
    "name": "sathiyajith",
    "rollno": 56,
    "cgpa": 8.6,
    "phone": "9976770500"
}

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

Output

Explanation: We create a dictionary and use json.dump() to directly write it to sample.json, skipping the need to manually convert it to a JSON string.

Python vs JSON Object Mapping

Related articles:

• JSON
• Serializing JSON
• dump()
• dumps()