Comprehensive Python Snippets: JSON Conversion, Date/Time Formatting, File I/O, QR & Barcode Generation, List & JSON Comparison, Class Reflection, and File Size Management

1. List to JSON and String to JSON – Use the built‑in json module to serialize a Python list or deserialize a JSON‑formatted string.

import json
my_list = ['apple', 'banana', 'cherry']
json_data = json.dumps(my_list)
print(json_data)  # ["apple", "banana", "cherry"]

my_string = '{"name": "John", "age": 30, "city": "New York"}'
json_data = json.loads(my_string)
print(json_data)  # {'name': 'John', 'age': 30, 'city': 'New York'}

Note: json.loads() returns a Python dict ; use json.dumps() to obtain a JSON string.

2. Date/Time Formatting – Convert between strings, datetime objects, and timestamps using the datetime module.

from datetime import datetime
# String to datetime object
string_time = '2022-04-21 13:30:00'
time_obj = datetime.strptime(string_time, '%Y-%m-%d %H:%M:%S')
print(time_obj)  # 2022-04-21 13:30:00

# Datetime object to string
time_obj = datetime.now()
string_time = time_obj.strftime('%Y-%m-%d %H:%M:%S')
print(string_time)  # e.g., 2023-04-21 16:52:22

# Timestamp to datetime and back
timestamp = 1650649800
time_obj = datetime.fromtimestamp(timestamp)
print(time_obj)  # 2022-12-21 12:30:00
timestamp = int(time_obj.timestamp())
print(timestamp)  # 1650649800

3. Reading Files – Open files with open() using relative or absolute paths; with ensures automatic closure.

# Read a file in the current directory
with open('example.txt', 'r') as f:
    content = f.read()
    print(content)

# Read a file using an absolute path
with open('/home/user/Documents/example.txt', 'r') as f:
    content = f.read()
    print(content)

For cross‑platform paths, prefer the os.path utilities.

4. QR‑Code Image Generation – The qrcode library creates QR codes with configurable version, error correction, box size, and border.

import qrcode
qr = qrcode.QRCode(version=1, error_correction=qrcode.constants.ERROR_CORRECT_L,
                 box_size=10, border=4)
data = 'https://www.example.com/'
qr.add_data(data)
qr.make(fit=True)
img = qr.make_image(fill_color='black', back_color='white')
img.save('qrcode.png')

Install the library with pip install qrcode .

5. Barcode Image Generation – Use the python-barcode package to generate EAN13 (or other) barcodes.

import barcode
from barcode.writer import ImageWriter

data = '123456789'
ean = barcode.get('ean13', data, writer=ImageWriter())
filename = ean.save('barcode')

Install with pip install python-barcode .

6. Bulk ID Card Generation – The id-validator library can create valid Chinese ID numbers.

from id_validator import validator
for i in range(10):
    id_card = validator.create_id_card()
    print(id_card)

Install with pip install id-validator . Use responsibly and comply with local regulations.

7. List Data Comparison – Compare two lists using set operations or list comprehensions.

# Using sets
list1 = [1, 2, 3, 4, 5]
list2 = [3, 4, 5, 6, 7]
set1, set2 = set(list1), set(list2)
intersection = list(set1.intersection(set2))
union = list(set1.union(set2))
difference = list(set1.difference(set2))
print(intersection, union, difference)

# Using list comprehensions
intersection = [x for x in list1 if x in list2]
union = list(set(list1 + list2))
difference = [x for x in list1 if x not in list2]
print(intersection, union, difference)

8. JSON Data Comparison – Parse JSON strings to Python objects and compare keys/values.

import json
json_str1 = '{"name": "Tom", "age": 18, "gender": "male"}'
json_str2 = '{"name": "Jerry", "age": 20, "gender": "male"}'
data1 = json.loads(json_str1)
data2 = json.loads(json_str2)
for key in data1:
    if key in data2:
        if data1[key] != data2[key]:
            print(key, "different:", data1[key], data2[key])
    else:
        print(key, "missing in second JSON")
for key in data2:
    if key not in data1:
        print(key, "missing in first JSON")

Ensure the JSON strings are well‑formed before loading.

9. Bulk Retrieval of Class Methods – Use reflection to list callable attributes of a class.

class MyClass:
    def __init__(self, name):
        self.name = name
    def my_method1(self):
        pass
    def my_method2(self):
        pass
    @classmethod
    def my_classmethod(cls):
        pass
    @staticmethod
    def my_staticmethod():
        pass

methods = [func for func in dir(MyClass) if callable(getattr(MyClass, func))]
for method in methods:
    print(method)

For detailed signatures, consider the inspect module.

10. File Size‑Based Automatic Cleanup – Continuously monitor a file and delete it when it exceeds a size limit, pausing between checks.

import os, time

def clear_file(file_path, limit_size=1024*1024, clear_interval=3600):
    """Delete the file when its size exceeds *limit_size*; repeat every *clear_interval* seconds."""
    while True:
        file_size = os.path.getsize(file_path)
        if file_size > limit_size:
            os.remove(file_path)
            print("File cleared:", file_path)
        else:
            print("File size within limit:", file_path)
        time.sleep(clear_interval)

# Example usage
clear_file("test.txt", limit_size=1024*1024, clear_interval=3600)

Handle potential exceptions (e.g., file in use) when integrating into production systems.