Read, Write and Parse JSON using Python

JSON is a lightweight data format for data interchange that can be easily read and written by humans, and easily parsed and generated by machines. It is a complete language-independent text format. To work with JSON data, Python has a built-in package called JSON.

Example of JSON String

s = '{"id":01, "name": "Emily", "language": ["C++", "Python"]}'

The syntax of JSON is considered a subset of the syntax of JavaScript including the following:

• Name/Value pairs: Represents Data, the name is followed by a colon(:), and the Name/Value pairs are separated by a comma(,).
• Curly braces: Holds objects.
• Square brackets: Hold arrays with values separated by a comma (,).

Keys/Name must be strings with double quotes and values must be data types amongst the following: 

• String
• Number
• Object (JSON object)
• array
• Boolean
• Null

Example of JSON file:

 {
   "employee": [
      {
         "id": "01",
         "name": "Amit",
         "department": "Sales"
      },
      {
         "id": "04",
         "name": "sunil",
         "department": "HR"
      }
   ]
}

Python Parse JSON String

In the below code, we are going to convert JSON to a Python object. To parse JSON string Python firstly we import the JSON module. We have a JSON string stored in a variable ’employee’ and we convert this JSON string to a Python object using json.loads() method of JSON module in Python. After that, we print the name of an employee using the key ‘name’ .

Python3

# Python program to convert JSON to Python
import json

# JSON string
employee ='{"id":"09", "name": "Nitin", "department":"Finance"}'

# Convert string to Python dict
employee_dict = json.loads(employee)
print(employee_dict)

print(employee_dict['name'])

Output

{'id': '09', 'name': 'Nitin', 'department': 'Finance'}
Nitin

Python read JSON file

Let’s suppose we have a JSON file that looks like this.

Here, we have used the open() function to read the JSON file. Then, the file is parsed using json.load() method which gives us a dictionary named data.

Python3

import json

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

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

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

# Closing file
f.close()

Output:

Convert Python Dict to JSON

In the below code, we are converting a Python dictionary to a JSON object using json.dumps() method of JSON module in Python. We first import the JSON module and then make a small dictionary with some key-value pairs and then passed it into json.dumps() method with ‘indent=4’ to convert this Python dictionary into a JSON object. As we have given the value of indent to 4 there are four whitespaces before each data as seen in the output.

Python3

# Python program to convert
# Python to JSON
import json

# Data to be written
dictionary = {
  "id": "04",
  "name": "sunil",
  "department": "HR"
}

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

Output

{
    "id": "04",
    "name": "sunil",
    "department": "HR"
}

The following types of Python objects can be converted into JSON strings: 

• dict
• list
• tuple
• string
• int
• float
• True
• False
• None

Python objects and their equivalent conversion to JSON:

Python	JSON Equivalent
dict	object
list, tuple	array
str	string
int, float	number
True	true
False	false
None	null

Writing JSON to a file in Python

We can write JSON to file using json.dump() function of JSON module and file handling in Python. In the below program, we have opened a file named sample.json in writing mode using ‘w’. The file will be created if it does not exist. Json.dump() will transform the Python dictionary to a JSON string and it will be saved in the file sample.json.

Python3

# Python program to write JSON
# to a file
import json

# Data to be written
dictionary ={
    "name" : "sathiyajith",
    "rollno" : 56,
    "cgpa" : 8.6,
    "phonenumber" : "9976770500"
}

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

Output:

Python Pretty Print JSON

When we convert a string to JSON the data is in a less readable format. To make it more readable we can use pretty printing by passing additional arguments in json.dumps() function such as indent and sort_keys as used in the below code.

Python3

# Python program to convert JSON to Python
import json

# JSON string
employee ='{"id":"09", "name": "Nitin", "department":"Finance"}'

# Convert string to Python dict
employee_dict = json.loads(employee)

# Pretty Printing JSON string back
print(json.dumps(employee_dict, indent = 4, sort_keys= True))

Output

{
    "department": "Finance",
    "id": "09",
    "name": "Nitin"
}