Python Code Snippets for Data Conversion, Date/Time Handling, File I/O, QR/Barcode Generation, List & JSON Comparison, and File Management

1. List and String to JSON – Use the built‑in json module.

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 that json.loads() returns a Python dict, while json.dumps() produces a JSON string.

2. Date‑Time Formatting – Convert between strings, datetime objects, and timestamps using datetime.strptime(), datetime.strftime(), and datetime.fromtimestamp() / datetime.timestamp(). Example:

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

now = datetime.now()
string_time = now.strftime('%Y-%m-%d %H:%M:%S')
print(string_time)

timestamp = 1650649800
time_obj = datetime.fromtimestamp(timestamp)
print(time_obj)

3. Reading Files – Use open() with a context manager. Relative path example:

with open('example.txt', 'r') as f:
    content = f.read()
    print(content)

Absolute path example uses the full file system path; for cross‑platform code, prefer os.path utilities.

4. QR Code Generation – Install qrcode ( pip install qrcode) and create an image:

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')

5. Barcode Generation – Install python-barcode ( pip install python-barcode) and generate an EAN13 barcode:

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

6. Bulk ID Card Generation – Use the id-validator library ( pip install id-validator) to create valid Chinese ID numbers:

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

7. List Comparison – Compare two lists using set operations or list comprehensions. Set example:

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

Comprehension example:

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]

8. JSON Data Comparison – Load two JSON strings with json.loads() and compare keys/values:

import json
json_str1 = '{"name": "Tom", "age": 18, "gender": "male"}'
json_str2 = '{"name": "Jerry", "age": 20, "gender": "male"}'
obj1 = json.loads(json_str1)
obj2 = json.loads(json_str2)
for key in obj1:
    if key in obj2:
        if obj1[key] != obj2[key]:
            print(key, "different:", obj1[key], obj2[key])
    else:
        print(key, "missing in second JSON")
for key in obj2:
    if key not in obj1:
        print(key, "missing in first JSON")

9. Retrieving All 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
    @classmethod
    def my_classmethod(cls):
        pass
    @staticmethod
    def my_staticmethod():
        pass
methods = [m for m in dir(MyClass) if callable(getattr(MyClass, m))]
for method in methods:
    print(method)

For detailed signatures, the inspect module can be used.

10. Automatic File Deletion When Size Exceeds 1 MB – Combine os and time to monitor a file and delete it at a fixed interval:

import os, time
def clear_file(file_path, limit_size=1024*1024, clear_interval=3600):
    while True:
        size = os.path.getsize(file_path)
        if size > limit_size:
            os.remove(file_path)
            print('File cleared:', file_path)
        else:
            print('File size OK:', file_path)
        time.sleep(clear_interval)
clear_file('test.txt')

Use with caution as deletion is irreversible.