JSON Module

The json module in Python provides functions for working with JSON data.

Task

Design a program that reads the value of the port attribute in the database.json file, changes it to 5432, and then writes it back to the file.

JavaScript implementation

import fs from 'fs';

// Read JSON file
fs.readFile('database.json', 'utf8', (err, data) => {
  if (err) {
    console.error(err);
    return;
  }

  try {
    // Parse JSON data into JavaScript object
    const jsonData = JSON.parse(data);

    // Change the value of the port attribute to 5432
    jsonData.port = 5432;

    // Convert JavaScript object back to JSON string
    const updatedData = JSON.stringify(jsonData, null, 2);

    // Write the updated JSON string back to the file
    fs.writeFile('database.json', updatedData, 'utf8', (err) => {
      if (err) {
        console.error(err);
        return;
      }

      console.log('JSON file has been updated');
    });
  } catch (err) {
    console.error('Failed to parse JSON file:', err);
  }
});

Python implementation

import json

# Read JSON file
with open('database.json', 'r') as file:
    json_data = json.load(file)

# Change the value of the port attribute to 5432
json_data['port'] = 5432

# Write the updated JSON data back to the file
with open('database.json', 'w') as file:
    json.dump(json_data, file, indent=2)

print('JSON file has been updated')

Code Highlight

• In Python, json.dumps() is used to convert objects to JSON strings, which is equivalent to JSON.stringify() in JavaScript.
• In Python, json.loads() is used to convert JSON strings to dictionaries, which is equivalent to JSON.parse() in JavaScript.

Chinese Encoding Issue

When converting Python objects to JSON strings, if you encounter Chinese encoding issues, you can use the ensure_ascii=False parameter to ensure that Chinese characters are encoded in their original Unicode form instead of ASCII encoding. For example:

import json

data = {"name": "Bob", "age": 25}
json_str = json.dumps(data, ensure_ascii=False)
print(json_str)

Difference Quick View

Feature	JavaScript	Python
Parse JSON string	JSON.parse(myStr)	json.loads(my_str)
Convert object to JSON string	JSON.stringify(myObj)	json.dumps(my_obj)
Read JSON file	-	json.load(my_file)
Write JSON file	-	json.dump(my_file)

danger

In Python, json.loads(my_str) and json.load(my_file) return a dictionary or list (depending on the structure of the JSON data). For dictionaries and nested dictionaries, note that Python syntax does not support using the dot operator (.) to access values. You need to use [] to access values.

import json

my_dict = json.loads('{"name": "luckrnx09", "age": 18}')
print(my_dict.name) # Error: 'dict' object has no attribute 'name'
print(my_dict['name']) # luckrnx09

Resources

• https://docs.python.org/3/library/json.html