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Copy-ready Python snippets by topic and difficulty — short, focused, and runnable in the browser editor.
Build a queue-based admission control system in Python
Implement a simple bounded-queue admission controller that accepts or rejects incoming requests based on current queue capacity.
from collections import deque
import time
class AdmissionControl:
"""Simple admission control using a bounded queue.
Requests arrive at the queue; they are admitted in FIFO order.
If the queue is full, the incoming request is rejected.
"""
def __init__(self, capacity: int):
self.capacit…Fixed Window Counter Rate Limiting in Python
A simple fixed window counter rate limiter that allows a maximum number of requests per 60-second window, with a mock time simulation.
from collections import deque
from time import time
class FixedWindowCounter:
def __init__(self, max_requests):
self.max_requests = max_requests
self.window_start = int(time())
self.window_count = 0
def allow_request(self):
current_time = int(time())
if current_time >=…How to Implement Hedged Requests in Python
This code demonstrates a hedged request pattern using threading, which sends duplicate calls and returns the first result that arrives within a timeout.
import time
from unittest.mock import Mock
def hedged_request(call, timeout=0.05):
"""Execute two duplicate calls, return first result within timeout."""
result_container = {}
def run_and_store():
result_container['result'] = call()
result_container['done'] = True
# Simulate slow cal…How to Implement a Token Bucket Rate Limiter per Client IP in Python
Implements a simple sliding-window rate limiter using a dictionary of timestamp lists per client IP to limit requests per window.
from time import time
from collections import defaultdict
class RateLimiter:
def __init__(self, max_requests: int, window_seconds: int):
self.max_requests = max_requests
self.window_seconds = window_seconds
self.clients = defaultdict(list)
def allow(self, ip: str) -> bool:
now…How to Stop Receiving Requests Until Ready in Python
A mock server that refuses requests until a readiness gate is passed, simulating fail-stop behavior for production reliability.
import random
import time
class MockServer:
def __init__(self):
self.ready = False
self.requests_received = 0
def readiness_check(self):
"""Simulates a readiness probe. Returns True only when ready."""
if not self.ready:
return False
return True
def r…How to implement rate limiting per API key in Python
A simple sliding-window rate limiter that tracks request timestamps per API key and rejects requests exceeding the configured limit.
import time
API_RATE_LIMITS = {"api_key_1": 5, "api_key_2": 3} # max requests per window
WINDOW_SECONDS = 10
class RateLimiter:
def __init__(self, limits, window):
self.limits = limits
self.window = window
self.requests = {key: [] for key in limits}
def allow(self, api_key):
…How to mock a fallback return value in Python
Test a function that returns a default value on failure by mocking requests.get and its side effects.
from unittest.mock import Mock, patch
import requests
def fetch_data(url, default=None):
try:
response = requests.get(url)
response.raise_for_status()
return response.json()
except (requests.RequestException, ValueError):
return default
with patch("requests.get") as mock_get:
…Rate Limit per User ID in Python with a Dict Mock
Implements a simple sliding window rate limiter using a defaultdict of timestamps per user ID, blocking requests that exceed a max count within a time window.
import time
from collections import defaultdict
class RateLimiter:
def __init__(self, max_requests, window_seconds):
self.max_requests = max_requests
self.window_seconds = window_seconds
self.user_timestamps = defaultdict(list)
def allow_request(self, user_id):
now = time.tim…Token bucket rate limiter in Python (in-memory)
Implement a thread-safe in-memory token bucket rate limiter that throttles requests based on a steady refill rate.
import time
import threading
class TokenBucket:
def __init__(self, capacity, refill_rate, refill_interval=1.0):
self.capacity = capacity
self.tokens = capacity
self.refill_rate = refill_rate
self.refill_interval = refill_interval
self.last_refill = time.monotonic()
…How to Ship Logs to an Aggregator Endpoint in Python
Ship batched log entries to a mock HTTP aggregator endpoint with proper error handling and response status.
import json
import requests
from datetime import datetime, timezone
LOG_ENTRIES = [
{"timestamp": "2024-01-15T10:00:00Z", "level": "INFO", "message": "Server started"},
{"timestamp": "2024-01-15T10:00:05Z", "level": "WARN", "message": "High memory usage"},
{"timestamp": "2024-01-15T10:00:10Z", "level": "E…How to Mock Service Versioning URI in Python
Run a minimal HTTP server in Python that routes requests to different versions of a service URI like /v1/users vs /v2/users.
from http.server import HTTPServer, BaseHTTPRequestHandler
import json
class VersionedHandler(BaseHTTPRequestHandler):
def _send_json(self, payload, status=200):
body = json.dumps(payload).encode("utf-8")
self.send_response(status)
self.send_header("Content-Type", "application/json")
…How to Mock an API Gateway Router in Python
Create a lightweight HTTP server that routes requests to mock microservice responses, simulating an API gateway for local development and testing.
from http.server import HTTPServer, BaseHTTPRequestHandler
import json
class SimpleGateway(BaseHTTPRequestHandler):
def do_GET(self):
routes = {
"/users": {"service": "user-service", "status": "ok", "count": 42},
"/orders": {"service": "order-service", "status": "ok", "count": 17}…How to Mock an Ambassador Edge Proxy in Python
Build a lightweight mock Ambassador edge proxy with Python's http.server that responds to health and user endpoint requests for local development and testing.
import http.server
import json
import urllib.parse
import threading
class AmbassadorProxyHandler(http.server.BaseHTTPRequestHandler):
def do_GET(self):
parsed = urllib.parse.urlparse(self.path)
if parsed.path == "/health":
self.send_response(200)
self.send_header("Content-T…How to implement read-your-writes sticky routing in Python
A mock StickyRouter class that routes all requests for the same key to the same node, ensuring read-after-write consistency.
import random
class StickyRouter:
def __init__(self, nodes):
self.nodes = nodes
self.routes = {}
def route(self, key):
if key not in self.routes:
self.routes[key] = random.choice(self.nodes)
return self.routes[key]
def read(self, key):
node = self.rout…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
…Retry idempotent GET requests in Python
A Python function that retries an idempotent GET request a fixed number of times with a delay between attempts, raising a RuntimeError only after all retries fail.
import time
import urllib.error
import urllib.request
from http.client import HTTPException
def fetch_with_retry(url, max_retries=3, delay=1.0):
for attempt in range(1, max_retries + 1):
try:
with urllib.request.urlopen(url, timeout=5) as response:
return response.read().decode…How to Create and Verify HMAC SHA256 API Signatures in Python
Generate and verify HMAC-SHA256 signatures for API requests using Python's hmac, hashlib, and base64 modules.
import hmac
import hashlib
import base64
import json
from datetime import datetime, timezone
def create_api_signature(secret_key: str, method: str, path: str, timestamp: str, body: dict = None) -> str:
"""Create HMAC-SHA256 signature for API request."""
payload = {
"method": method.upper(),
"p…How to mock resource request limits in Python
A Python class that simulates CPU and memory limit checks for resource requests, returning clear acceptance or rejection messages.
class ResourceLimits:
def __init__(self, cpu_limit, memory_limit):
self.cpu_limit = cpu_limit
self.memory_limit = memory_limit
def check_request(self, cpu, memory):
if cpu > self.cpu_limit:
return "CPU limit exceeded: {cpu} > {limit}".format(cpu=cpu, limit=self.cpu_limit)
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