Python Code
Samples
Medium snippets you can copy, study, and run in the browser editor.
How to Use asyncio Lock to Protect a Shared Counter in Python
This code demonstrates how to use an asyncio.Lock to safely increment a shared counter from multiple concurrent coroutines.
import asyncio
async def increment(counter, lock, increments):
for _ in range(increments):
async with lock:
counter[0] += 1
async def main():
counter = [0]
lock = asyncio.Lock()
tasks = [
increment(counter, lock, 1000)
for _ in range(5)
]
await asyncio.gath…Build a BFF (Backend for Frontend) Mock Aggregator in Python
A minimal HTTP server implementing the BFF pattern that aggregates user data and orders from two mock backends into a single JSON response.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
from urllib.parse import urlparse
class MockBackendA:
def get_user(self, user_id):
return {"id": user_id, "name": "Alice", "service": "backend-a"}
class MockBackendB:
def get_orders(self, user_id):
return [
{…How to Build an Adapter to Translate External API Responses in Python
Build an adapter class that translates a mock external API's response shape into your internal representation, keeping callers decoupled from the external contract.
import json
from typing import Dict, Any
class ExternalAPI:
"""Mock external service returning a different data shape."""
def get_user(self, user_id: int) -> Dict[str, Any]:
return {
"id": user_id,
"full_name": "Jane Doe",
"email_address": "jane@example.com",
…How to Structure a Three-Tier Layered Architecture in Python
A mock three-tier architecture with presentation, business, and data layers that process a user request from input to response.
class PresentationLayer:
def __init__(self, business_layer):
self.business = business_layer
def handle_request(self, user_id):
print(f"[Presentation] Received request for user {user_id}")
data = self.business.process_user(user_id)
print(f"[Presentation] Response: {data}")
…Implement Bulkhead Thread Pool Isolation in Python
Create isolated thread pools with a bulkhead pattern to protect different services from cascading failures.
import threading
import time
import random
from concurrent.futures import ThreadPoolExecutor
class Bulkhead:
"""Simple bulkhead isolation: separate thread pools for different tasks."""
def __init__(self, max_workers):
self.executor = ThreadPoolExecutor(max_workers=max_workers)
self.active = …How to Handle Retry-After Header in Python
Parse the Retry-After header from rate-limited API responses and implement retry logic with proper delays in Python.
```python
import time
from datetime import datetime, timedelta
class RetryAfterHandler:
def __init__(self, max_retries=3):
self.max_retries = max_retries
def get_retry_after_seconds(self, response_headers):
retry_after_value = response_headers.get("Retry-After")
if retry_after_value …Implement If-Match Precondition Update in Python
A mock resource store that uses the If-Match header's ETag to guard updates, preventing overwrites from stale clients.
from dataclasses import dataclass
from typing import Optional
@dataclass
class Resource:
id: str
version: int = 1
data: str = ""
etag: str = "etag-1"
class MockResourceStore:
def __init__(self):
self.resources = {}
def update(self, resource_id: str, new_data: str, if_match: Optiona…How to Read Redis Streams with XREADGROUP in Python
Read new messages from a Redis stream using a consumer group with XREADGROUP, handling JSON payloads and group creation.
import redis
import json
def read_group_messages(stream_key, group_name, consumer_name, count=10):
r = redis.Redis(host="localhost", port=6379, decode_responses=True)
try:
r.xgroup_create(stream_key, group_name, id="0", mkstream=True)
except redis.exceptions.ResponseError:
pass
messag…How to Track Cache Hit Ratio in Python
Simulate an LRU cache with hit/miss tracking and compute a real-time hit ratio from random access patterns.
import random
import time
from collections import OrderedDict
class LRUCache:
def __init__(self, capacity: int):
self.cache = OrderedDict()
self.capacity = capacity
self.hits = 0
self.misses = 0
def get(self, key):
if key in self.cache:
self.hits += 1
…How to Mock ROC AUC in Python
Compute ROC AUC from scratch in Python using pairwise comparisons between positive and negative score distributions, ideal for testing ML models without sklearn.
import random
from math import comb
def mock_roc_auc(scores, labels):
"""Compute mock ROC AUC by simulating a classifier's score distribution."""
random.seed(42)
n = len(labels)
pos_scores = [scores[i] for i in range(n) if labels[i] == 1]
neg_scores = [scores[i] for i in range(n) if labels[i] == …K-Fold Cross Validation in Python: A Simple Implementation
Implements k-fold cross validation from scratch, splitting data into folds and computing MSE scores for a baseline mean-predictor model.
import random
from statistics import mean
def cross_validation_scores(data, labels, k=5, seed=42):
random.seed(seed)
indices = list(range(len(data)))
random.shuffle(indices)
fold_size = len(indices) // k
folds = []
for i in range(k):
if i == k - 1:
folds.append(indices[i *…Train Logistic Regression From Scratch in Python
Trains a binary logistic regression model using gradient descent on mock data, printing learned weights and probabilities.
import numpy as np
# Mock data: 2 features, binary classification
X = np.array([[1, 2], [2, 3], [3, 4], [4, 5], [5, 6]])
y = np.array([0, 0, 1, 1, 1])
# Add bias term (column of ones)
X_b = np.c_[np.ones((X.shape[0], 1)), X]
# Initialize parameters
theta = np.zeros(X_b.shape[1])
# Hyperparameters
learning_rate = 0…Check Sample Ratio Mismatch in Python
Estimates the probability that a simple random sample's proportion differs from the population proportion by more than 10% using simulation.
import random
def sample_ratio_mismatch(population_size: int, sample_size: int, p: float) -> float:
"""
Estimate the probability that a simple random sample's proportion
differs from the population proportion by more than 10%.
"""
total_counts = [0, 0]
for _ in range(10000):
sample = …Synthetic Control in Python: Mock Example
Implements synthetic control from scratch: learns donor weights via ridge regression on pre-period data, then predicts a counterfactual for the treated unit.
import numpy as np
class SyntheticControl:
def __init__(self, data, treated_index, pre_periods, post_periods):
self.data = np.array(data, dtype=float)
self.treated_index = treated_index
self.pre_periods = pre_periods
self.post_periods = post_periods
def fit_weights(sel…How to Create a Covering Index with INCLUDE Columns in Python
Create a covering index with INCLUDE columns in SQLite from Python and inspect the query plan to confirm the index covers the query.
import sqlite3
def create_covering_index_mock():
conn = sqlite3.connect(":memory:")
cursor = conn.cursor()
cursor.execute("""
CREATE TABLE employees (
id INTEGER PRIMARY KEY,
name TEXT,
department TEXT,
salary INTEGER
)
""")
employe…Mock CQRS Read/Write Split in Python
Separate order mutations from queries using a read model and write model to mock CQRS-style separation of concerns.
from dataclasses import dataclass, field
from typing import List, Dict
@dataclass
class Order:
id: int
amount: float
status: str = "pending"
class OrderWriteModel:
"""Handles all mutations (writes) to orders."""
def __init__(self):
self._orders: Dict[int, Order] = {}
self._next…How to Mock Environment Variables in Python for 12-Factor Config
Read 12-factor config from env vars and test/mock them with unittest.mock.patch.dict without touching the real environment.
import os
import json
from unittest.mock import patch
def load_config(env_prefix="APP"):
"""Read 12-factor style config from env vars"""
required = ["DATABASE_URL", "API_KEY"]
optional = {"PORT": "8080", "DEBUG": "false"}
config = {}
for key in required:
full_key = f"{env_prefix}_{key…How to Mock HTTP Responses to Verify HSTS Headers in Python
This code demonstrates how to use unittest.mock to intercept and capture HTTP response headers, specifically the Strict-Transport-Security header, from a mocked HTTPServer handler for security validation.
from http.server import BaseHTTPRequestHandler, HTTPServer
from unittest.mock import patch
class StrictTransportMock(BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
self.send_header("Strict-Transport-Security", "max-age=31536000; includeSubDomains")
self.end_headers()
…How to redact secrets from log messages in Python
This code defines a logging.Filter subclass that automatically redacts sensitive keys like password, token, and API key from any dict logged.
import logging
from dataclasses import dataclass
@dataclass
class ApiResponse:
status: int
body: dict
class SecretRedactor(logging.Filter):
SENSITIVE_KEYS = {"password", "token", "secret", "api_key"}
def filter(self, record: logging.LogRecord) -> bool:
if isinstance(record.msg, dict):
…Implement RSA OAEP Padding in Python
Implements OAEP-style padding with MGF1 using SHA-256 from the Python standard library for RSA encryption prep.
import os
import hashlib
def mgf1(seed, length, hash_func=hashlib.sha256):
"""MGF1 mask generation function."""
output = b""
counter = 0
while len(output) < length:
c = counter.to_bytes(4, "big")
output += hash_func(seed + c).digest()
counter += 1
return output[:length]
…Mock ConfigMap Mount Environment Variables in Python
Simulate reading environment variables from a Kubernetes ConfigMap-mounted directory and test it with mocks.
import os
import tempfile
from unittest.mock import patch
def load_config_from_mount(mount_path):
"""Simulate reading environment variables from a ConfigMap-mounted directory."""
config = {}
for filename in os.listdir(mount_path):
file_path = os.path.join(mount_path, filename)
if os.path.i…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.