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JSON Module

What is JSON?

JSON (JavaScript Object Notation) is a format for structuring data.
JSON is a lightweight, text-based data interchange format that is completely language-independent.
Similar to XML, JSON is a format for structuring data commonly used by web applications to communicate with each other.

Why JSON?

Whenever we declare a variable and assign a value to it, the variable itself doesn't hold the value. Instead, the variable holds an address in memory where the value is stored. For example:

age = 21

When we use age, it gets replaced with 21. However, age doesn't contain 21, it contains the address of the memory location where 21 is stored.
While this works locally, transferring this data, such as through an API, poses a challenge. Sending your computer’s entire memory with the addresses is impractical and insecure. This is where JSON comes to the rescue.

Example JSON

JSON supports most widely used data types including String , Number, Boolean, Null, Array and Object.
Here is an example of JSON file

{
  "name": "John Doe",
  "age": 21,
  "isStudent": true,
  "address": null,
  "courses": ["Math", "Science", "History"],
  "grades": {
    "Math": 95,
    "Science": 89,
    "History": 76
  }
}

Python JSON

Python too supports JSON with a built-in package called json. This package provides all the necessary tools for working with JSON Objects including parsing, serializing, deserializing, and many more.

1. Python parse JSON string.

To parse JSON string Python firstly we import the JSON module.
JSON string is converted to a Python object using json.loads() method of JSON module in Python.
Example Code:

# Python program to convert JSON to Python
import json

# JSON string
students ='{"id":"01", "name": "Yatharth", "department":"Computer Science Engineering"}'

# Convert string to Python dict
students_dict = json.loads(students)
print(students_dict)

print(students_dict['name'])

Ouput:

{"id": "01", "name": "Yatharth", "department": "Computer Science Engineering"}

2. Python load JSON file.

JSON data can also be directly fetch from a json file
Example:

import json
# Opening JSON file
f = open('input.json',)

# Returns JSON object as a dictionary
data = json.load(f)

# Iterating through the json file
for i in data['students']:
    print(i)

# Closing file
f.close()

JSON file

{
  "students":{
    {
      "id": "01", 
      "name": "Yatharth", 
      "department": "Computer Science Engineering"
    },
     {
      "id": "02", 
      "name": "Raj", 
      "department": "Mechanical Engineering"
    }
  }
}

Ouput

{"id": "01", "name": "Yatharth", "department": "Computer Science Engineering"}
{"id": "02", "name": "Raj", "department": "Mechanical Engineering"}

json.load(): Reads JSON data from a file object and deserializes it into a Python object.
json.loads(): Deserializes JSON data from a string into a Python object.

Addtiotnal Context

Relation between python data types and json data types is given in table below.

Python Object	JSON Object
Dict	object
list, tuple	array
str	string
int, long, float	numbers
True	true
False	false
None	null

3. Python Dictionary to JSON String

Parsing python dictionary to json string using json.dumps().
Example Code:

import json 
    
# Data to be written 
dictionary ={ 
  "id": "03", 
  "name": "Suraj", 
  "department": "Civil Engineering"
} 

# Serializing json  
json_object = json.dumps(dictionary, indent = 4) 
print(json_object)

Output:

{
    "department": "Civil Engineering",
    "id": "02",
    "name": "Suraj"
}

4. Python Dictionary to JSON file.

- Parsing python dictionary to json string using json.dump().
Example Code:

import json

# Data to be written
dictionary ={
	"name" : "Satyendra",
	"rollno" : 51,
	"cgpa" : 8.8,
	"phonenumber" : "123456789"
}

with open("sample.json", "w") as outfile:
	json.dump(dictionary, outfile)

Ouput: sample.json

{
	"name" : "Satyendra",
	"rollno" : 51,
	"cgpa" : 8.8,
	"phonenumber" : "123456789"
}

5. Append Python Dictionary to JSON String.

Append to an already existing string using json.update().
Example :

import json
# JSON data:
x = { 
  "id": "03", 
  "name": "Suraj"
} 

# python object to be appended
y = { "department": "Civil Engineering"}

# parsing JSON string:
z = json.loads(x)

# appending the data
z.update(y)

# the result is a JSON string:
print(json.dumps(z))

Ouput:

{"id": "03", "name": "Suraj", "department": "Civil Engineering"}

6. Append Python Dictionary to JSON File.

There is no direct function to append in file. So, we will load file in a dictionary, update dictionary then update content and convert back to json file format.
data.json

{
  "students":{
    {
      "id": "01", 
      "name": "Yatharth", 
      "department": "Computer Science Engineering"
    },
     {
      "id": "02", 
      "name": "Raj", 
      "department": "Mechanical Engineering"
    } 
  }
}

Example Code:

import json

# function to add to JSON
def write_json(new_data, filename='data.json'):
    with open(filename,'r+') as file:
        # First we load existing data into a dict.
        file_data = json.load(file)
        # Join new_data with file_data inside students
        file_data["students"].append(new_data)
        # Sets file's current position at offset.
        file.seek(0)
        # convert back to json.
        json.dump(file_data, file, indent = 4)

# python object to be appended
y = { 
  "id": "03", 
  "name": "Suraj", 
  "department": "Civil Engineering"
} 
    
write_json(y)

Output:

{
  "students":{
    {
      "id": "01", 
      "name": "Yatharth", 
      "department": "Computer Science Engineering"
    },
     {
      "id": "02", 
      "name": "Raj", 
      "department": "Mechanical Engineering"
    },
    { 
      "id": "03", 
      "name": "Suraj", 
      "department": "Civil Engineering"
    } 
  }
}

The Python json module simplifies the handling of JSON data, offering a bridge between Python data structures and JSON representations, vital for data exchange and storage in modern applications.

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