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Python JSON

  • Post category:python
  • Reading time:5 mins read

What is JSON?

JSON (JavaScript Object Notation) is a lightweight data interchange format that’s easy for humans to read and write, and easy for machines to parse and generate. Python has a built-in module called json that can be used to work with JSON data.

Let’s begin with a basic example and convert a JSON string to a Dictionary:

# Import json module.
import json

data = '{"name": "Shivaay Singh Chauhan", "age": 6, "city": "Haridwar"}'

# Loading a JSON data as a Dictionary.
data_dict = json.loads(data)

# iterating over the dictionary items and printing key, value pairs.
for key, value in data_dict.items():
    print(key, "=", value)

# Output
name = Shivaay Singh Chauhan
age = 6
city = Haridwar

In this example, we have loaded a JSON string to a python dictionary. Let’s see how to convert a python dictionary to a JSON string.

# Python Dictionary to a JSON string.
data = {
    "name": "Shivaay Singh Chauhan",
    "age": 6,
    "city": "Haridwar"
}

dict_json = json.dumps(data)
print("dict to json: ", dict_json)

#Output
dict to json:  {"name": "Shivaay Singh Chauhan", "age": 6, "city": "Haridwar"}

Reading JSON from a file

To read JSON data from a file and convert it into a Python dictionary, you can use the json.load() method.

demo.json file:

{
  "name": "Shivaay Singh Chauhan",
  "age": 6,
  "city": "Haridwar"
}

Python Code:

import json
data = {}
with open("demo.json","r") as file:
    data = json.load(file)

print(data)
print(type(data))

# Output
{'name': 'Shivaay Singh Chauhan', 'age': 6, 'city': 'Haridwar'}
<class 'dict'>

Writing JSON to a File

To write a Python dictionary to a file in JSON format, you can use the json.dump() method.

import json

person_dict = {"name": "Shivaay Singh Chauhan",
               "languages": ["Hindi", "English"],
               "married": False,
               "age": 6
               }

with open("person.txt", "w") as json_file:
    json.dump(person_dict, json_file)

Pretty Printing JSON

To pretty print a JSON string, you can use the indent parameter in the json.dumps() method.

  • You can use the indent parameter to define the numbers of indents.
  • You can separators, default value is (“, “, “: “), which means using a comma and a space to separate each object, and a colon and a space to separate key and value.
# Python Dictionary to a JSON string.
data = {
    "name": "Shivaay Singh Chauhan",
    "age": 6,
    "city": "Haridwar"
}

# Use the indent parameter to define the numbers of indents.
dict_json = json.dumps(data, indent=4, separators=("$ ", " :: "))
print("dict json: ", dict_json)

# Output
dict json:  {
    "name" :: "Shivaay Singh Chauhan"$ 
    "age" :: 6$ 
    "city" :: "Haridwar"
}

You can also sort the result by using `sort_keys` paramter:

# Python Dictionary to a JSON string.
data = {
    "name": "Shivaay Singh Chauhan",
    "age": 6,
    "city": "Haridwar"
}

# Use the indent parameter to define the numbers of indents.
dict_json = json.dumps(data, indent=4, separators=("$ ", " :: "), sort_keys=True)
print("dict json: ", dict_json)

# Output
dict json:  {
    "name" :: "Shivaay Singh Chauhan"$ 
    "age" :: 6$ 
    "city" :: "Haridwar"
}

# Output
dict json:  {
    "age" :: 6$ 
    "city" :: "Haridwar"$ 
    "name" :: "Shivaay Singh Chauhan"
}

Using custom serializer for complex data-types

import json
from datetime import datetime


# Custom serializer for complex data-types like datetime.
def custom_serializer(value):
    if isinstance(value, datetime):
        # Converting a datetime into string ISO 8601 format.
        return value.isoformat()
    raise TypeError("Value is not Serializable.")


# the key joined has a value of type 'datetime.datetime'.
data = {
    "name": "John",
    "age": 30,
    "joined": datetime.now()
}

json_string = json.dumps(data, default=custom_serializer)
print(json_string)


# Output
{"name": "John", "age": 30, "joined": "2024-06-16T19:49:02.535075"}

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