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Python JSON serialization basics

JSON (JavaScript Object Notation) is a fundamental standard for data structures in software engineering.^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md] It is widely used for data storage and transfer, such as in HTTP Web APIs, application configuration files, and database storage.^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]

JSON Syntax

JSON structures data using specific syntax rules:^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]

  • Objects: Defined by curly braces {}.
  • Arrays (Lists): Defined by square brackets [].
  • Format: Keys and values are enclosed in double quotes, separated by a colon.

In Python, JSON objects typically map to dictionaries, and JSON arrays map to lists.

The json Library

Python includes a built-in json library for handling JSON data serialization and deserialization^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].

  • json.dumps(): Converts a Python object (typically a dictionary) into a JSON formatted string^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].
  • json.loads(): Parses a JSON formatted string back into a Python dictionary^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].

Serialization Constraints

The json.dumps() function has specific requirements regarding the input data type^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]. It can serialize standard data types like strings and numbers, but it cannot directly serialize custom objects.^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]

If you attempt to serialize a custom class instance, it will raise a TypeError: Object of type ... is not JSON serializable^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]. To successfully serialize custom objects, they must first be converted into a dictionary format^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].

Working with Custom Objects

To serialize custom objects to JSON, the data must be transformed from a class instance to a standard dictionary^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]. A common method to achieve this in Python is using the __dict__ attribute^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].

For example, a Customer object can be converted into a dictionary like so:^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md]

# Converting a list of objects to a dictionary structure for JSON
customerDict = {}
for id in customers:
    customerDict[id] = customers[id].__dict__

jsonData = json.dumps(customerDict)

File I/O Operations

The typical workflow for persisting data involves reading from and writing to .json files^[400-devops__09-Scripting-Language__python__introduction__part-3.json__README.md].

Writing JSON: 

import json

def updateCustomers(customer):
    with open('customers.json', 'w', newline='') as customerFile:
        customerJSON = json.dumps(customer)
        customerFile.write(customerJSON)

Reading JSON: 

import json
import os.path

def getCustomers():
    if os.path.isfile("customers.json"):
        with open('customers.json', newline='') as customerFile:
            data = customerFile.read()
            customers = json.loads(data)
            return customers
    else:
        return {}

  • File I/O
  • [[Dictionaries]]
  • [[HTTP Web APIs]]

Sources