Python Code
Samples
Easy snippets you can copy, study, and run in the browser editor.
How to Mock a Failing Dependency to Test Error Paths in Python
Inject a fake HTTP client that raises a connection error to test how code handles dependency failures without touching the network.
import requests
def fetch_user(user_id):
url = f"https://api.example.com/users/{user_id}"
response = requests.get(url, timeout=5)
response.raise_for_status()
return response.json()
def get_user_name(user_id, http_client):
try:
user_data = http_client(user_id)
return user_data["nam…How to Mock an LLM Client in Python
Create a simple mock LLM client that returns a canned completion for testing or development without a real API.
from dataclasses import dataclass
@dataclass
class MockLLMClient:
canned_response: str = "This is a canned completion."
def complete(self, prompt: str) -> str:
return f"{self.canned_response} [to: {prompt[:20]}]"
if __name__ == "__main__":
client = MockLLMClient()
result = client.complete(…Parse nginx access log top IPs in Python
Reads an nginx access log line by line, extracts the client IP, and returns the most frequent IPs using a regex and Counter.
import re
from collections import Counter
def top_ips(log_file, n=10):
ip_pattern = re.compile(r'^(\S+)')
ip_counts = Counter()
with open(log_file, 'r') as f:
for line in f:
match = ip_pattern.match(line)
if match:
ip_counts[match.group(1)] += 1
return…How to Test HTTPX Async Client Pool Reuse with Mocks in Python
Mock an httpx.AsyncClient to verify connection pool reuse by asserting GET calls share a single client instance across concurrent async requests.
import asyncio
import httpx
from unittest.mock import AsyncMock, patch, Mock
async def fetch_with_pool(client, url, n_reuses=3):
results = []
for i in range(n_reuses):
resp = await client.get(url)
results.append(resp.status_code)
await asyncio.sleep(0) # yield to loop to mimic real us…How to Mock the Ambassador Pattern Retry Client in Python
This code demonstrates the ambassador pattern for API clients by simulating a flaky request and retrying with exponential backoff, useful for testing resilience in system design.
import time
import random
class RetryingClient:
"""Retry wrapper simulating a flaky ambassador-style API client."""
def __init__(self, max_attempts=3, base_delay=0.1):
self.max_attempts = max_attempts
self.base_delay = base_delay
self.attempts = 0
def _flaky_request(self):
…How to Mock MQTT Topic Subscriptions with QoS in Python
Build a lightweight MQTT client mock that tracks topic subscriptions with QoS levels and simulates wildcard message delivery.
import time
from collections import defaultdict
class MockMQTTClient:
def __init__(self):
self.subscriptions = defaultdict(list)
self.messages = []
def subscribe(self, topic, qos=0):
self.subscriptions[topic].append(qos)
print(f"Subscribed to '{topic}' with QoS {qos}")
…Cache Data in Redis with Python
A beginner-friendly Redis cache helper that stores JSON strings with a TTL and retrieves them with the redis-py client.
import redis
class DataCache:
def __init__(self, host="localhost", port=6379, db=0):
self.client = redis.Redis(host=host, port=port, db=db, decode_responses=True)
def cache_data(self, key, value, ttl=60):
self.client.setex(key, ttl, value)
def get_cached_data(self, key):
return …How to Iterate Redis Keys with SCAN in Python
Iterate all Redis keys matching a pattern using the SCAN command with a mock client to simulate pagination.
import redis
def scan_keys(client, pattern="*", count=10):
keys = []
cursor = 0
while True:
cursor, batch = client.scan(cursor=cursor, match=pattern, count=count)
keys.extend(batch)
if cursor == 0:
break
return keys
if __name__ == "__main__":
# Mock Redis clien…How to Use Redis as a Cache in Python
A beginner-friendly RedisCache helper that stores, retrieves, and deletes JSON values with automatic TTL expiration using the redis-py client.
import json
import time
import redis
class RedisCache:
def __init__(self, host="localhost", port=6379, db=0, default_ttl=60):
self.client = redis.Redis(host=host, port=port, db=db, decode_responses=True)
self.default_ttl = default_ttl
def set(self, key, value, ttl=None):
"""Store a v…How to Mock HTTP Client Latency in Python
Simulate outbound HTTP request latency with configurable ranges to test timeouts, retries, and SLO monitoring without external services.
import time
import random
def mock_latency(host: str, min_ms: int = 100, max_ms: int = 500) -> dict:
"""Simulate an outbound HTTP request with mock latency."""
latency_ms = random.randint(min_ms, max_ms)
start = time.perf_counter()
time.sleep(latency_ms / 1000)
elapsed_ms = (time.perf_counter() - …How to implement round-robin load balancing in Python
Implement a client-side round-robin load balancer that distributes requests sequentially across a list of mock servers using itertools.cycle.
import itertools
import random
class MockServer:
def __init__(self, name):
self.name = name
def handle_request(self, request_id):
return f"Server {self.name} handled request #{request_id}"
class RoundRobinLoadBalancer:
def __init__(self, servers):
self.servers = servers
…How to mock an external service in Python with an anti-corruption facade
This code implements an anti-corruption facade that mocks an external API, allowing client code to interact with a simulated service while keeping the same interface.
class AntiCorruptionFacade:
"""Mocks a real API while keeping the same interface."""
def __init__(self, data_store):
self._data_store = data_store
self._calls = []
def get_user(self, user_id):
self._calls.append(f"get_user({user_id})")
return self._data_store.get(u…Enforce TLS 1.2 Minimum in Python
Create an SSL context with a minimum TLS version of 1.2 to enforce secure connections.
import ssl
def get_min_tls_version():
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.minimum_version = ssl.TLSVersion.TLSv1_2
return context.minimum_version
if __name__ == "__main__":
min_version = get_min_tls_version()
print(f"Minimum TLS version set to: {min_version.name} (value: {mi…How to Set X-Frame-Options DENY in Flask with a Mock Response
Set the X-Frame-Options header to DENY in a Flask response to prevent clickjacking, and verify it with Flask's test client.
from flask import Flask, Response
app = Flask(__name__)
@app.route("/")
def index():
response = Response("Hello, World!")
response.headers["X-Frame-Options"] = "DENY"
return response
if __name__ == "__main__":
with app.test_client() as client:
resp = client.get("/")
print(resp.get_da…Browse by section
Each section groups closely related Python snippets.
Guide: free Python code samples library
Copy-ready Python snippets for learners and developers
PythonSkillset code samples are short, focused examples organised by topic and difficulty. Every snippet is server-rendered HTML — readable by search engines and easy to copy. Open any sample, read the notes, copy the code, then press Try in editor to run it in the browser with Pyodide.
How to use this library
- Pick a topic section — strings, lists, files, functions, and more
- Open a sample, read How it works, and copy the code block
- Run it in the IDE, tweak values, then take a related quiz or tutorial lesson
Samples vs tutorials and challenges
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.