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How to Escape HTML in Python
This code demonstrates how to use Python's `html.escape` function to safely encode user input for display in HTML, preventing XSS attacks.
import html
def escape_user_input(user_input: str) -> str:
"""Escape HTML-sensitive characters for safe display."""
return html.escape(user_input)
if __name__ == "__main__":
sample_user_input = '<script>alert("XSS")</script> & \'quotes\''
safe_output = escape_user_input(sample_user_input)
print("…How to Use Keyword-Only Arguments in Python Functions
Define Python functions with keyword-only arguments using the * separator to enforce clarity and prevent positional misuse.
def greet(name, *, greeting="Hello", punctuation="!"):
"""Greet someone with a customizable message using keyword-only arguments."""
message = f"{greeting}, {name}{punctuation}"
return message
if __name__ == "__main__":
# Basic call with only the positional argument
print(greet("Alice"))
# Al…Parameterize SQL queries in Python to prevent SQL injection
Safely fetch users from a SQLite database using parameterized queries to prevent SQL injection attacks.
import sqlite3
def get_users_by_name(name):
"""Fetch users safely using parameterized query."""
conn = sqlite3.connect(':memory:')
cursor = conn.cursor()
# Create sample table and data
cursor.execute('CREATE TABLE users (id INTEGER, name TEXT)')
cursor.executemany('INSERT INTO users (name…How to Invert a Dictionary in Python Safely
Swap dictionary keys and values while detecting duplicate values to prevent silent data loss.
def invert_dict_safely(d):
inverted = {}
for key, value in d.items():
if value not in inverted:
inverted[value] = key
else:
raise ValueError(f"Duplicate value '{value}' would cause data loss")
return inverted
if __name__ == "__main__":
sample = {"a": 1, "b": 2,…How to Create Immutable Data Classes with frozen=True in Python
Create immutable data classes in Python using @dataclass(frozen=True) to prevent attribute modifications after instantiation.
from dataclasses import dataclass
@dataclass(frozen=True)
class Point:
x: float
y: float
def distance_from_origin(self) -> float:
return (self.x**2 + self.y**2) ** 0.5
if __name__ == "__main__":
p = Point(3.0, 4.0)
print(p)
print(f"Distance from origin: {p.distance_from_origin():.2f}…Slots Class: How to Reduce Memory Usage in Python
Use __slots__ to prevent dynamic attribute creation and reduce per-instance memory overhead, while keeping methods intact.
class SlotsDemo:
__slots__ = ("name", "age", "email")
def __init__(self, name, age, email):
self.name = name
self.age = age
self.email = email
def describe(self):
return f"{self.name}, {self.age}, {self.email}"
if __name__ == "__main__":
instance = SlotsDemo("Alice", …Build a Live Countdown Timer for Events in Python
A Python script that displays a real-time countdown to a target date and time, updating every second in the console.
import datetime
import time
def countdown(event_name, target_datetime):
"""Displays a live countdown to a target datetime."""
while True:
now = datetime.datetime.now()
remaining = target_datetime - now
if remaining.total_seconds() <= 0:
print(f"\n🚀 {event_name} is happening…Generate a Monthly Report CSV from Log Files in Python
Reads a CSV log file, filters events by a given month, aggregates daily event counts and revenue, and writes a summarized monthly report to a new CSV.
import csv
from collections import defaultdict
from datetime import datetime
def generate_monthly_report(log_file: str, month: str, output_file: str) -> None:
events_by_date = defaultdict(int)
revenue_by_date = defaultdict(float)
with open(log_file, 'r') as f:
for line in f:
date_…Enrich Events with Geo IP Data in Python
Returns a copy of each event dictionary, enriched with a geo-location dict from a mock IP-to-geo lookup table, with a fallback for unknown IPs.
import ipaddress
GEO_IP_DB = {
"192.168.1.10": {"country": "US", "city": "New York", "lat": 40.7128, "lon": -74.0060},
"10.0.0.5": {"country": "DE", "city": "Berlin", "lat": 52.5200, "lon": 13.4050},
"172.16.0.8": {"country": "JP", "city": "Tokyo", "lat": 35.6762, "lon": 139.6503},
}
EVENTS = [
{"id…Group Python Events into Sessions with a Gap Timeout
Groups timestamped events into sessions, starting a new session when the time gap exceeds a specified timeout.
from itertools import groupby
from datetime import datetime, timedelta
def session_window_group(events, gap_seconds=300):
"""Group events into sessions where gap > gap_seconds starts a new session."""
if not events:
return []
events = sorted(events, key=lambda x: x[0])
sessions = []
c…How to Deduplicate Events with At-Least-Once Delivery in Python
Implements an exactly-once processing pattern for at-least-once event delivery by tracking seen event IDs in a set, skipping duplicates.
seen_ids = set()
def process_event(event_id: str, payload: dict) -> dict:
"""Process an event exactly once, ignoring duplicates."""
if event_id in seen_ids:
return {"status": "duplicate", "event_id": event_id}
seen_ids.add(event_id)
return {"status": "processed", "event_id": event_id, **payloa…How to route late-arriving data to a side output in Python
Separate late-arriving events from a streaming data batch into a dead-letter side output list using a timestamp threshold.
from collections import defaultdict
def late_arriving_side_output(events, late_threshold_ts):
"""
Mock a streaming pipeline that separates late-arriving data events
into a side output list (e.g., for dead-letter analysis).
events: list of (timestamp, data) tuples, timestamps as ints.
late_thresho…Generate Mock CloudFormation Stack Events in Python
Generate a list of mock AWS CloudFormation stack events with random resources, statuses, and timestamps, and print them as JSON.
import json
import random
from datetime import datetime, timedelta
def generate_mock_stack_events(stack_name="MyTestStack", num_events=10):
"""Generate a list of mock CloudFormation stack events."""
resources = [
("AWS::S3::Bucket", "MyBucket"),
("AWS::EC2::Instance", "MyInstance"),
("…How to Mock Auto Scaling Policy Scale Out in Python
Define a mock auto-scaling function that scales out capacity by a factor up to a max, simulating AWS-like events.
def mock_scale_out(current_capacity: int, max_capacity: int, scale_factor: int = 1) -> tuple:
"""
Mock auto-scaling policy: scales out by the specified factor
if capacity allows, capped at max_capacity.
"""
if current_capacity >= max_capacity:
return current_capacity, False
new_cap…How to Mock GCP Cloud Functions HTTP Events in Python
Simulate a GCP Cloud Functions HTTP event with a Python mock handler that constructs a realistic event payload and returns a JSON response.
import json
from datetime import datetime, timezone
def mock_http_event(data):
"""Simulate a GCP Cloud Function HTTP event."""
event = {
"event_id": "mock-event-12345",
"timestamp": datetime.now(timezone.utc).isoformat(),
"event_type": "google.cloud.functions.http",
"resource"…How to Parse an AWS API Gateway Proxy Event in Python
Extract and parse common fields from a mock API Gateway proxy event, turning the JSON body into a native Python dict.
import json
from typing import Any, Dict, Optional
def parse_proxy_event(event: Dict[str, Any]) -> Dict[str, Any]:
"""Extract and parse common fields from an API Gateway proxy event."""
body = event.get("body", "")
if isinstance(body, str):
body = json.loads(body) if body else {}
elif body is…Mock Lambda handler event context dict in Python
Simulates an AWS Lambda invocation by passing a mock event dict and context object to a handler, then prints the response.
import json
def lambda_handler(event, context):
"""
A mock AWS Lambda handler that processes an event dict and context object.
Demonstrates the typical Lambda function signature and basic event/context usage.
"""
print("Received event:", json.dumps(event, indent=2))
print("Function name:", co…How to Initialize Sentry SDK with a Mock DSN in Python
Initialize the Sentry SDK in Python with a mock DSN to test error tracking without sending real events, then verify the DSN configuration.
import sentry_sdk
# Initialize Sentry SDK with a mock DSN (no real events will be sent)
sentry_sdk.init(
dsn="https://mock-public@mock-host/mock-project",
traces_sample_rate=1.0,
environment="development",
)
# Capture a test message to confirm SDK is configured
sentry_sdk.capture_message("Test message fr…How to Run an Async Main with asyncio.run in Python
Show the canonical entry point for an asyncio program: define an async main, then launch it with asyncio.run.
import asyncio
async def main():
print("Hello from async main")
await asyncio.sleep(0.1)
print("Done")
if __name__ == "__main__":
asyncio.run(main())How to Signal asyncio Workers to Stop with an Event in Python
Use an asyncio.Event to coordinate graceful shutdown of multiple concurrent worker tasks in Python.
import asyncio
import random
async def worker(name, stop_event):
while not stop_event.is_set():
await asyncio.sleep(random.uniform(0.1, 0.5))
print(f"Worker {name} processing...")
print(f"Worker {name} stopped.")
async def main():
stop_event = asyncio.Event()
workers = [asyncio.create…How to Use threading.Lock to Synchronize a Counter in Python
Safely increment a shared counter across multiple threads using threading.Lock as a mutex to prevent race conditions.
import threading
counter = 0
lock = threading.Lock()
def increment():
global counter
for _ in range(100000):
with lock:
counter += 1
threads = [threading.Thread(target=increment) for _ in range(5)]
for t in threads:
t.start()
for t in threads:
t.join()
print(f"Final counter valu…How to Use uvloop Faster Event Loop
Install uvloop at startup to replace asyncio's default event loop with a faster libuv-based one, with a graceful fallback when it's unavailable.
import asyncio
try:
import uvloop
uvloop.install()
USING_UVLOOP = True
except ImportError:
USING_UVLOOP = False
async def fetch_data(index):
await asyncio.sleep(0.01)
return f"data-{index}"
async def main():
tasks = [fetch_data(i) for i in range(10)]
results = await asyncio.gather(*…How to set a timeout with asyncio.wait_for in Python
Use asyncio.wait_for to bound an async function with a timeout, catching TimeoutError when it exceeds the limit.
import asyncio
async def slow_task():
await asyncio.sleep(3)
return "finished"
async def main():
try:
result = await asyncio.wait_for(slow_task(), timeout=1)
print(result)
except asyncio.TimeoutError:
print("Task timed out")
if __name__ == "__main__":
asyncio.run(main())Run Background Tasks with asyncio.create_task in Python
Create background tasks in an asyncio event loop with asyncio.create_task and run them concurrently using asyncio.gather.
import asyncio
import time
async def background_worker(name, duration):
"""Simulates a long-running background task."""
print(f"{name} started at t={time.monotonic():.1f}")
await asyncio.sleep(duration)
print(f"{name} finished at t={time.monotonic():.1f}")
async def main():
print(f"Main starting …Browse by section
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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.