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Implement a Consistent Hash Ring in Python
Build a minimal consistent hash ring with virtual nodes to map keys to servers stably as nodes are added or removed.
import hashlib
import bisect
class ConsistentHashRing:
def __init__(self, nodes=None, replicas=3):
self.replicas = replicas
self.ring = {}
self.sorted_keys = []
if nodes:
for node in nodes:
self.add_node(node)
def _hash(self, key):
return i…Build a Bulk Array POST Mock Server in Python
Creates an HTTP mock server that accepts POST requests with a JSON array and returns incremental IDs for each item.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
from urllib.parse import urlparse
class MockHandler(BaseHTTPRequestHandler):
def do_POST(self):
if urlparse(self.path).path != "/bulk":
self.send_response(404)
self.end_headers()
return
cont…Build a Mock REST API with PUT and GET in Python
A minimal mock REST server implementing idempotent PUT for resource replacement and GET for retrieval, built with Python's http.server module.
from http.server import BaseHTTPRequestHandler, HTTPServer
import json
from urllib.parse import urlparse
mock_db = {}
class MockAPIHandler(BaseHTTPRequestHandler):
def do_PUT(self):
parsed = urlparse(self.path)
resource_id = parsed.path.strip("/").split("/")[-1]
content_length = int(self.…How to Build Cursor Pagination with Next and Prev Tokens in Python
A minimal cursor pagination implementation that returns next and previous cursor tokens for navigating a dataset.
from pprint import pprint
def make_cursor(page):
return f"page:{page:04d}"
def parse_cursor(cursor):
_, page = cursor.split(":", 1)
return int(page)
def paginate(all_items, page_size, cursor=None):
start = parse_cursor(cursor) if cursor else 0
end = start + page_size
items = all_items[sta…How to Build a Batch Operations Multi-Status 207 Mock Server in Python
Build a mock HTTP server that accepts a batch of operations and returns HTTP 207 Multi-Status with per-operation status codes in JSON.
from http.server import BaseHTTPRequestHandler, HTTPServer
import json
class BatchHandler(BaseHTTPRequestHandler):
def do_POST(self):
if self.path != "/batch":
self.send_response(404)
self.end_headers()
return
content_length = int(self.headers.get("Content-Leng…How to Build a Hypermedia Collection Resource in Python
Creates a paginated hypermedia collection resource with HATEOAS links and embedded items.
import json
import math
class HypermediaCollection:
"""A mock hypermedia collection resource."""
def __init__(self, items, base_url="/api/items"):
self.items = items
self.base_url = base_url
def to_dict(self, page=1, per_page=3):
total = len(self.items)
pages = math.ceil…How to Build a Mock REST GET Endpoint Handler in Python
Create a lightweight mock REST GET server in Python using the standard library, with a dict-based route registry that maps paths to handler functions and returns JSON responses with proper HTTP status codes.
from http.server import BaseHTTPRequestHandler, HTTPServer
import json
# Mock API handler registry
def handle_users():
return {"status": "ok", "data": [{"id": 1, "name": "Alice"}, {"id": 2, "name": "Bob"}]}
def handle_products():
return {"status": "ok", "data": [{"id": 101, "name": "Laptop", "price": 999.99}…How to Build an Idempotency-Key POST Handler in Python
Python HTTP server mock that accepts POST requests and deduplicates them using an Idempotency-Key header, returning the same response for repeated calls.
import hashlib
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
from urllib.parse import urlparse
class MockAPI(BaseHTTPRequestHandler):
responses = {}
def do_POST(self):
length = int(self.headers.get("Content-Length", 0))
body = self.rfile.read(length).decode("utf-8")
…How to Implement Content Negotiation with JSON and XML in Python
Build an HTTP server that returns JSON or XML responses based on the client's Accept header, with a 406 response for unsupported formats.
import json
import xml.etree.ElementTree as ET
from http.server import BaseHTTPRequestHandler, HTTPServer
class RequestHandler(BaseHTTPRequestHandler):
def do_GET(self):
data = {"message": "Hello, world!"}
accept_header = self.headers.get("Accept", "")
if "application/json" in accept_hea…How to Implement ETag Optimistic Concurrency in Python
Build a lightweight in-memory resource store that uses MD5 hash ETags to prevent lost updates via optimistic concurrency control.
import hashlib
import json
class ResourceStore:
def __init__(self):
self.data = {}
self.etags = {}
def get(self, resource_id):
if resource_id not in self.data:
return None, None
return self.data[resource_id], self.etags[resource_id]
def put(self, resource_id, …How to Mock a 202 Accepted Long-Running Operation in Python
Build a mock HTTP server that returns a 202 Accepted response immediately and simulates a long-running operation in the background with threading.
import time
import threading
from http.server import HTTPServer, BaseHTTPRequestHandler
class MockHandler(BaseHTTPRequestHandler):
def do_POST(self):
if self.path == "/long-running":
self.send_response(202)
self.send_header("Content-Type", "application/json")
self.end_h…How to Mock a Chunked Encoding Streaming Response in Python
Build a local mock HTTP server with Python's http.server that streams a chunked-encoded response with a 0.5s delay per chunk.
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
import time
class ChunkedHandler(BaseHTTPRequestHandler):
protocol_version = "HTTP/1.1"
def do_GET(self):
self.send_response(200)
self.send_header("Content-Type", "text/plain")
self.send_header("Transfer-Encoding", "c…How to Validate Request Body JSON Against a Schema in Python
Build a lightweight schema validator to check required fields, types, string lengths, allowed values, and nested objects in a JSON request body.
import json
def validate_against_schema(data, schema, path=""):
errors = []
if not isinstance(data, dict):
errors.append(f"{path}: expected object, got {type(data).__name__}")
return errors
for field, rules in schema.items():
field_path = f"{path}.{field}" if path else field
…Version API by Accept Header with Vendor Media Types in Python
Build a mock HTTP server that routes to API versions by parsing vendor-specific Accept headers in Python.
from http.client import HTTPMessage
from http.server import BaseHTTPRequestHandler, HTTPServer
class VendorVersionHandler(BaseHTTPRequestHandler):
def do_GET(self):
accept = self.headers.get("Accept", "")
version = "v1"
if "application/vnd.myapi.v2+json" in accept:
version = "…How to Build a Flow Control Credit Window in Python
A Python class that reserves, confirms, releases, and settles credit to limit message flow and prevent overload in streaming pipelines.
class CreditWindow:
def __init__(self, max_credit=1000):
self.max_credit = max_credit
self.used_credit = 0
self.pending_credit = 0
def try_reserve(self, amount):
available = self.max_credit - self.used_credit - self.pending_credit
if available >= amount:
…How to Mock NATS Subject Hierarchies with Wildcards in Python
Build a lightweight NATS-style pub/sub mock that matches subject hierarchies with '*' and '>' wildcards for tests or prototypes.
# Mock a simplified NATS subject hierarchy with wildcard matching
# Supports: exact match, '*' (single token), '>' (tail wildcard)
class NATSSubjectMock:
def __init__(self):
self.subscriptions = {} # subject -> list of callbacks
def subscribe(self, subject, callback):
self.subscriptions.setd…How to mock a CQRS projector read model update in Python
Build a CQRS projector class that maintains denormalized read models by applying domain events in a mock order-processing service.
from dataclasses import dataclass, field
from typing import Dict, List, Optional
@dataclass
class OrderReadModel:
order_id: str
customer_name: str
total: float
status: str = "pending"
items: List[Dict] = field(default_factory=list)
def apply_event(self, event_type: str, payload: Dict) -> Non…In-Memory PubSub Topic Subscribe Mock in Python
Build a thread-safe in-memory publish/subscribe mock where handlers subscribe to named topics and receive every message published to them.
class PubSub:
def __init__(self):
self.topics = {}
def subscribe(self, topic, callback):
if topic not in self.topics:
self.topics[topic] = []
self.topics[topic].append(callback)
def publish(self, topic, message):
for callback in self.topics.get(topic, []):
…How to Build a Bloom Filter to Reduce Cache Misses in Python
Implement a probabilistic Bloom filter in Python that lets a cache quickly determine which keys are definitely not present, reducing expensive source lookups on cache misses.
import hashlib
import random
class BloomFilter:
def __init__(self, size=100, num_hashes=3):
self.size = size
self.num_hashes = num_hashes
self.bit_array = [0] * size
def _hashes(self, item):
result = []
for i in range(self.num_hashes):
hash_value = int(hash…How to Cache Data in Redis with Python
Build a simple Redis cache wrapper that stores and retrieves JSON data with automatic TTL and serialization.
import redis
import json
import time
class Cache:
def __init__(self, host="localhost", port=6379, db=0, default_ttl=60):
self.client = redis.Redis(host=host, port=port, db=db)
self.default_ttl = default_ttl
def get(self, key):
value = self.client.get(key)
if value is None:
…How to Implement a Redis-Like Cache Dictionary in Python
Build a RedisMockDict class that mimics basic Redis key-value operations with TTL support, expiry cleanup, and standard dict-like methods.
from collections import OrderedDict
import time
class RedisMockDict:
def __init__(self, ttl=None):
self._data = OrderedDict()
self._ttl = ttl # default TTL in seconds, None = no expiry
self._expiry = {}
def set(self, key, value, ttl=None):
"""Set a key-value pair with optiona…How to implement a write-behind cache with async queue in Python
Build an async write-behind cache that queues writes in memory and flushes them in batches to persistent storage.
import asyncio
from collections import deque
from dataclasses import dataclass
@dataclass
class CacheEntry:
key: str
value: str
class WriteBehindCache:
def __init__(self, flush_interval=1.0):
self.cache = {}
self.queue = deque()
self.flush_interval = flush_interval
self._f…How to Cap Retry Attempts in Python with a Decorator
Build a reusable retry decorator that caps attempts, adds delays, and lets flaky services fail fast instead of hanging.
import random
from functools import wraps
from time import sleep
def retry(max_attempts, delay=0.1):
def decorator(func):
@wraps(func)
def wrapper(*args, **kwargs):
attempts = 0
while attempts < max_attempts:
try:
return func(*args, **kw…How to Implement an Adaptive Rate Limiter in Python
Build an adaptive rate limiter that adjusts request intervals dynamically based on recent error rates, slowing down when failures spike.
import time
import random
class AdaptiveRateLimiter:
"""Simple adaptive rate limiter that reduces requests when error rate is high."""
def __init__(self, min_interval=0.1, max_interval=2.0, error_threshold=0.3):
self.min_interval = min_interval
self.max_interval = max_interval
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