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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
Extract URLs from text with regex in Python
Uses a regular expression to find and print HTTP/HTTPS URLs from a block of text.
import re
text = """
Visit https://www.example.com for docs.
Contact support@mysite.org.
Check http://localhost:8000/api or ftp://files.example.net.
"""
url_pattern = r'https?://[^\s]+'
urls = re.findall(url_pattern, text)
for url in urls:
print(url)Catch RecursionError and Fail Gracefully in Python
Wrap a recursive function call in a try-except block to catch RecursionError and print a graceful failure message instead of crashing.
def compute_factorial_recursive(n):
"""Compute factorial recursively, raising RecursionError for deep recursion."""
if n == 0:
return 1
return n * compute_factorial_recursive(n - 1)
if __name__ == "__main__":
try:
result = compute_factorial_recursive(10000)
print(f"Factorial c…Catch ValueError and print friendly message in Python
Wrap an int() call in a try/except block and print a friendly message when ValueError is raised.
try:
number = int("not_a_number")
except ValueError:
print("That's not a valid number. Please enter digits only.")How to Build a Simple Debug Timer in Python
Create a context manager class to time the execution of a code block with a one-line printout.
import time
class DebugTimer:
"""Context manager that times the execution of a code block."""
def __init__(self, label="Operation"):
self.label = label
self.start_time = None
def __enter__(self):
self.start_time = time.perf_counter()
return self
def __exit__(self, e…How to Catch ValueError in Python (try except)
Handle invalid numeric input by catching ValueError in a try/except block and returning a friendly error message.
def parse_number(text):
try:
number = int(text)
return f"Parsed number: {number}"
except ValueError as error:
return f"Error: '{text}' is not a valid number ({error})"
if __name__ == "__main__":
examples = ["42", "hello", "3.14", "100"]
for item in examples:
print(pars…How to Handle ValueError Exceptions in Python
A beginner-friendly example showing how to catch ValueError and related exceptions with try-except blocks in Python.
def divide_numbers(a, b):
try:
result = a / b
return f"{a} / {b} = {result}"
except ZeroDivisionError:
return "Error: Cannot divide by zero."
except TypeError:
return "Error: Please provide numbers, not strings."
except ValueError:
return "Error: Invalid value de…How to Handle ValueError When Converting Strings to Integers in Python
Convert text to an integer with a try-except block that catches ValueError and prints beginner-friendly error messages.
def parse_number(text):
"""Convert text to an integer, showing beginner-friendly error handling."""
try:
number = int(text)
print(f"Successfully parsed: {number}")
return number
except ValueError as e:
print(f"Error: '{text}' is not a valid number.")
print(f"Debuggin…How to Handle ValueError and Multiple Exceptions in Python
This code demonstrates try/except blocks for beginners, handling ZeroDivisionError, TypeError, and ValueError with two practical functions: dividing numbers and parsing strings to floats.
def divide_numbers(a, b):
"""Divide two numbers with error handling for beginners."""
try:
result = a / b
print(f"{a} / {b} = {result}")
return result
except ZeroDivisionError:
print(f"Error: Cannot divide {a} by zero!")
except TypeError:
print(f"Error: Both argu…How to Handle ValueError in Python (try except)
Learn to catch ValueError and other exceptions with try-except blocks in Python using practical division and string-to-float conversion examples.
def divide_numbers(a, b):
"""Divide two numbers and handle ValueError safely."""
try:
result = a / b
return f"{a} / {b} = {result}"
except ZeroDivisionError:
return "Error: Cannot divide by zero!"
except TypeError:
return "Error: Both inputs must be numbers!"
def parse…How to Handle ValueError with try-except in Python
Build a beginner-friendly division calculator that catches ValueError and ZeroDivisionError with try-except blocks.
def get_number(prompt="Enter a number: "):
while True:
try:
value = float(input(prompt))
return value
except ValueError:
print("That's not a valid number. Please try again.")
def divide_numbers(a, b):
try:
result = a / b
return result
ex…How to Inspect Local Variables in an except Block in Python
Capture and print local variables at the moment an exception occurs using locals() inside an except block.
def risky_operation(value):
try:
result = 10 / value
return result
except ZeroDivisionError as e:
local_vars = dict(locals())
print(f"Error: {e}")
print("Local variables at exception:")
for key, val in local_vars.items():
print(f" {key} = {val}")
…How to Use try except else finally in Python
Demonstrates the correct order of try/except/else/finally blocks in Python with a safe division function.
def safe_divide(numerator, denominator):
try:
result = numerator / denominator
except ZeroDivisionError:
print("Error: Cannot divide by zero!")
except TypeError:
print("Error: Both arguments must be numbers!")
else:
print(f"Division successful: {numerator} / {denominator…Implement circuit breaker open after failures demo in Python
A minimal CircuitBreaker class that calls a function and automatically 'opens' after a set number of consecutive failures, blocking further calls with a RuntimeError.
import time
from datetime import datetime
class CircuitBreaker:
def __init__(self, threshold=3):
self.threshold = threshold
self.failure_count = 0
self.is_open = False
def call(self, func, *args, **kwargs):
if self.is_open:
raise RuntimeError("Circuit is OPEN")
…Split try except ValueError handler for beginners in Python
Demonstrates how to handle ValueError and ZeroDivisionError separately using try/except blocks, with beginner-friendly examples for parsing and division.
def parse_number(text):
try:
number = int(text)
return f"Parsed successfully: {number}"
except ValueError as error:
return f"Conversion failed: {error}"
def divide_numbers(dividend, divisor):
try:
result = dividend / divisor
return f"Division result: {result}"
e…Chunk Large File Upload Simulation by Blocks in Python
A Python script reads a large binary file in fixed-size chunks and simulates a block-by-block upload with per-chunk SHA256 hashing.
import os
import hashlib
from pathlib import Path
def read_file_in_chunks(file_path, chunk_size=8196):
"""Yield chunks of a file as bytes."""
with open(file_path, 'rb') as f:
while chunk := f.read(chunk_size):
yield chunk
def simulate_chunked_upload(file_path, chunk_size=8196):
"""S…How to Use fcntl for Exclusive File Locking in Python
This code demonstrates how to acquire an exclusive advisory lock on a file using fcntl.flock with a non-blocking flag, simulate work, then release the lock.
import fcntl
import os
import tempfile
import time
def acquire_exclusive_lock(filepath):
fd = os.open(filepath, os.O_RDWR | os.O_CREAT)
try:
fcntl.flock(fd, fcntl.LOCK_EX | fcntl.LOCK_NB)
print(f"Exclusive lock acquired on {filepath}")
time.sleep(1) # Simulate work while holding the l…How to define a custom exception class in Python with an error code attribute
Create a custom exception class with extra attributes like an error code, then raise and catch it in a try/except block.
class UserNotFoundError(Exception):
def __init__(self, user_id, error_code=404):
self.user_id = user_id
self.error_code = error_code
super().__init__(f"User with ID {user_id} was not found (error code: {error_code})")
def find_user(user_id, users_db):
if user_id not in users_db:
…How to Close a Generator and Handle GeneratorExit in Python
This Python code demonstrates how to explicitly close a generator using the close() method and handle the GeneratorExit exception through a finally block to run cleanup logic.
def countdown(n):
try:
while n > 0:
yield n
n -= 1
finally:
print(f"Generator closed after countdown completed")
if __name__ == "__main__":
gen = countdown(5)
print(next(gen))
print(next(gen))
gen.close()
print("Generator closed explicitly")How to Filter Blocked Words in Python
Scans input text against a moderation blocklist, returning blocked terms and their counts.
MODERATION_BLOCKLIST = {"spam", "scam", "fraud", "phishing", "malware", "abuse"}
def scan_text(text: str) -> dict:
normalized = text.lower()
words = normalized.replace(".", " ").replace(",", " ").replace("!", " ").replace("?", " ").split()
found_terms = []
for word in words:
if word in MO…How to Update a Hosts File to Block Distractions in Python
This script updates a local hosts file (or a demo file) by adding or updating entries to block distracting websites like Facebook and Twitter.
from pathlib import Path
def update_hosts(entries):
"""
Add or update blocking entries in the hosts file.
Uses a local demo file by default to avoid system changes.
"""
hosts_path = Path("demo_hosts.txt")
# Create demo file if it doesn't exist
if not hosts_path.exists():
hosts…How to Write an IP Block List to hosts.deny in Python
This Python script validates a list of IP addresses and CIDR ranges, then writes them to a hosts.deny file to block connections at the TCP wrapper level.
from ipaddress import ip_network
def write_hosts_deny(ip_list, output_file="hosts.deny"):
with open(output_file, "w") as f:
for ip in ip_list:
try:
ip_network(ip)
f.write(f"ALL: {ip}\n")
except ValueError:
continue
print(f"Written…How to check Python files for common coding mistakes
Walks a directory tree parsing each .py file with ast, reporting empty functions, bare try blocks, too many parameters, and empty classes.
import ast
import os
import sys
def check_file(filepath):
try:
with open(filepath) as f:
code = f.read()
tree = ast.parse(code, filename=filepath)
except SyntaxError as e:
print(f"{filepath}: SyntaxError: {e.msg}")
return
issues = []
for node in ast.wal…Mock pip-compile to Resolve Requirements in Python
A mock function that mimics pip-compile by converting a requirements.in file into pinned, locked package versions.
import subprocess
import tempfile
from pathlib import Path
def compile_requirements_mock(requirements_in: str) -> str:
"""Mock pip-compile: resolve a simple requirements.in into a locked format."""
lines = [line.strip() for line in requirements_in.splitlines() if line.strip() and not line.startswith("#")]
…How to Demonstrate the GIL with Python Threads vs Processes
Measure and compare wall-clock time for CPU-bound work using Python threads (limited by the GIL) versus multiprocessing (which bypasses the GIL).
import threading
import multiprocessing
import time
import os
def cpu_heavy(n):
return sum(i * i for i in range(n))
def run_threads(n):
threads = [threading.Thread(target=cpu_heavy, args=(n,)) for _ in range(2)]
start = time.perf_counter()
for t in threads:
t.start()
for t in threads:
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- Open a sample, read How it works, and copy the code block
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Samples are quick reference — one concept per page. For step-by-step teaching, use our Python tutorials. To test yourself, try quizzes or coding challenges. Clean up style with the Python formatter.