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.