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Inbox pattern consumer dedupe mock in Python
Implements a mock inbox consumer that deduplicates incoming messages by ID, with automatic eviction of old seen IDs to prevent unbounded memory growth.
import json
from collections import deque
from dataclasses import dataclass, field
from hashlib import sha256
from typing import Any
@dataclass
class InboxConsumer:
max_seen: int = 1000
seen_ids: set = field(default_factory=set)
seen_history: deque = field(default_factory=deque)
def _mark_seen(self,…Lazy loading with a proxy in Python: defer expensive service creation
A lazy proxy defers creating an expensive service object until its method is first called, then caches it for reuse.
import time
import random
class ExpensiveService:
def __init__(self, name):
self.name = name
print(f"Creating expensive service: {self.name}")
def fetch_data(self):
time.sleep(1)
return f"Data from {self.name}: {random.randint(1, 100)}"
class LazyProxy:
def __init__(sel…Microkernel Plug-in Core Mock in Python
Implements a minimal microkernel plug-in core that registers, unregisters, and executes synchronous or asynchronous plugins via a pluggable manager class.
import json
import abc
import inspect
class MicrokernelCore(abc.ABC):
def __init__(self):
self._plugins = {}
def register(self, name, plugin):
self._plugins[name] = plugin
def unregister(self, name):
return self._plugins.pop(name, None)
def execute(self, name, *args, **kwa…Mock Unit of Work commit and rollback in Python
Verify that a Unit of Work pattern commits on success and rolls back on failure using unittest.mock in Python.
from unittest import mock
class UnitOfWork:
def __init__(self):
self.committed = False
self.rolled_back = False
def commit(self):
self.committed = True
print("Commit executed")
def rollback(self):
self.rolled_back = True
print("Rollback executed")
def b…Object Pool Pattern for Database Connections in Python
Implements a reusable connection pool with acquire/release and context manager support, mocking database connections with idle reuse and exhaustion handling.
import time
from contextlib import contextmanager
from collections import deque
class ConnectionPool:
def __init__(self, size=3, max_idle=5):
self._idle = deque(maxlen=max_idle)
self._active = set()
self.size = size
def _create(self):
return {"created_at": time.time(), "queri…Outbox pattern reliable publish in Python with SQLite
Implements a transactional outbox with SQLite, ensuring reliable message publishing by storing events in the same DB transaction as business changes.
import sqlite3
from contextlib import contextmanager
from datetime import datetime, timezone
class Outbox:
def __init__(self, db_path=":memory:"):
self.conn = sqlite3.connect(db_path)
self.conn.execute("""
CREATE TABLE IF NOT EXISTS outbox (
id INTEGER PRIMARY KEY AUTO…Simulate a Leaky Bucket Rate Limiter in Python
This code implements a leaky bucket rate limiter that drains at a fixed rate and accepts or rejects incoming requests based on capacity.
import time
from collections import deque
class LeakyBucket:
"""Simulates a leaky bucket rate limiter with a fixed drain rate."""
def __init__(self, capacity, drain_rate_per_sec):
self.capacity = capacity
self.drain_rate = drain_rate_per_sec
self.water = 0.0
self.last_refill =…Singleton Config Loader in Python with Caution
Implements a singleton config loader in Python that reads JSON config files, but demonstrates the hidden gotcha of shared state across instances.
import json
from pathlib import Path
class ConfigLoader:
_instance = None
def __new__(cls, *args, **kwargs):
if cls._instance is None:
cls._instance = super().__new__(cls)
return cls._instance
def __init__(self, config_file="config.json"):
if not hasattr(self, "loaded…Template Method Workflow Steps Base Class in Python
Define a reusable workflow skeleton in a base class and let subclasses fill in each step with the Template Method design pattern.
from abc import ABC, abstractmethod
class DataPipeline(ABC):
"""Template Method pattern: defines a workflow skeleton."""
def run(self):
"""Template method - defines the algorithm's structure."""
result = {"extracted": False, "transformed": False, "loaded": False}
raw_data = self._ext…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 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 …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 OAuth2 Bearer Token Auth Middleware in Python
Create a simple OAuth2 bearer token authentication middleware that verifies signed tokens and enforces scope-based access control.
import hmac
import time
import base64
import json
from functools import wraps
VALID_TOKENS = {"test_token_123": {"user": "alice", "scope": "read:posts"}}
def generate_token(username: str) -> str:
payload = {"user": username, "iat": int(time.time())}
encoded = base64.urlsafe_b64encode(json.dumps(payload).enc…How to Mock X-RateLimit Headers in Python
This code creates a local HTTP server that mimics rate limit headers (X-RateLimit-Limit, Remaining, Reset, Update) and returns 429 responses when the limit is exceeded.
import time
import threading
from http.server import BaseHTTPRequestHandler, HTTPServer
class RateLimitHandler(BaseHTTPRequestHandler):
RATE_LIMIT = 5 # max requests allowed
WINDOW_SECONDS = 60 # per time window
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
…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 Mock a Webhook Subscribe Callback URL in Python
Mock a webhook subscribe callback URL using Python's http.server to receive and parse POST requests sent by webhook providers.
import json
from http.server import BaseHTTPRequestHandler, HTTPServer
class WebhookHandler(BaseHTTPRequestHandler):
def do_POST(self):
content_length = int(self.headers.get('Content-Length', 0))
payload = json.loads(self.rfile.read(content_length)) if content_length else {}
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