Reliability & rate limiting
Retries, exponential backoff, circuit breakers, token buckets, and idempotent handlers.
How to Implement Graceful Degradation with Feature Disabling in Python
A pattern that disables enhanced features and falls back to basic functionality when a dependency fails, with mock-based testing.
import random
from unittest.mock import patch
class EnhancedFeature:
"""A feature that can gracefully degrade when a dependency is unavailable."""
def __init__(self):
self.feature_enabled = True
def get_enhanced_data(self):
"""Simulate an enhanced feature that depends on external data."…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 Bulkhead Pattern with Threading in Python
Implement a bulkhead pattern in Python that isolates concurrent tasks with a bounded semaphore, limiting active workers to prevent resource exhaustion.
import threading
import time
import random
class Bulkhead:
def __init__(self, workers: int):
self._semaphore = threading.BoundedSemaphore(workers)
self._lock = threading.Lock()
self._active = 0
def run(self, task):
with self._semaphore:
with self._lock:
…How to Implement a Circuit Breaker in Python
A Python dataclass that provides circuit breaker logic with closed, open, and half-open states to fail fast on repeated errors.
from dataclasses import dataclass
from datetime import datetime, timedelta
import time
@dataclass
class CircuitBreaker:
failure_threshold: int = 3
timeout_seconds: float = 5.0
failures: int = 0
state: str = "closed"
last_failure: datetime = None
def call(self, func):
if self.state ==…How to Implement a Temporary Block in Python
Build a reusable PenaltyBox class that temporarily blocks access after a failure and reports remaining lockout time.
class PenaltyBox:
def __init__(self, block_seconds: int = 30):
self.block_seconds = block_seconds
self._blocked_until = 0.0
self._attempts = 0
def try_access(self, current_time: float) -> bool:
if self._blocked_until and current_time < self._blocked_until:
return Fa…How to Mock a Try Confirm Cancel Pattern in Python
Define a simple class with confirm and cancel methods, execute a try confirm with error handling, and print the final state.
class TCC:
def __init__(self):
self.confirmed = False
self.cancelled = False
def confirm(self):
self.confirmed = True
return "confirmed"
def cancel(self):
self.cancelled = True
return "cancelled"
def try_confirm(self):
try:
result =…How to Retry on Specific Exception Tuples in Python
A decorator-based retry pattern that retries a function only when it raises exceptions specified in a tuple, with configurable retries and delay.
import time
import random
from unittest.mock import patch
def retry_on_exceptions(retries=3, exceptions=(ValueError,), delay=0.1):
def decorator(func):
def wrapper(*args, **kwargs):
for attempt in range(retries):
try:
return func(*args, **kwargs)
…How to Simulate an Outbox Pattern with Reliable Retry in Python
This code implements a mock outbox pattern with records, delivery attempts, and retries to simulate reliable message publishing.
import time
import itertools
class Outbox:
def __init__(self):
self._records = []
self._seq = itertools.count(1)
def publish(self, topic, payload):
record = {
"id": next(self._seq),
"topic": topic,
"payload": payload,
"status": "pending"…Implement a Circuit Breaker Pattern in Python
This code implements a simple circuit breaker that opens after a threshold of consecutive failures, causing subsequent calls to fail fast without invoking the underlying function.
class CircuitBreaker:
def __init__(self, failure_threshold=3):
self.failure_threshold = failure_threshold
self.failure_count = 0
self.open = False
def call(self, func, *args, **kwargs):
if self.open:
raise RuntimeError("Circuit is open - failing fast")
try:
…Implementing Fallback with Cached Stale Data in Python
This code demonstrates a resilient data-fetching pattern that caches successful responses, falls back to cached data when the external API fails, and returns stale data as a last-resort fallback.
import random
import time
# Simulated cache dictionary: key -> (value, timestamp)
_cache = {}
_CACHE_TTL = 3 # seconds
# Mock data source (simulates an unreliable external API)
def fetch_mock_data(key):
failure = random.random() < 0.4 # 40% chance of failure
if failure:
raise ConnectionError("Mock …Rate Limiting with Queue Rejection in Python
Simulates a load shed pattern that rejects tasks when a queue fills up.
from collections import deque
import time
class RateLimiter:
def __init__(self, max_queue_size=3):
self.queue = deque()
self.max_queue_size = max_queue_size
self.rejected_count = 0
def submit(self, task_name):
if len(self.queue) >= self.max_queue_size:
self.reject…Saga Compensating Transaction Mock in Python
Simulates a distributed transaction using a saga pattern with compensating actions that roll back steps on failure.
import random
import time
class OrderService:
def __init__(self):
self.orders = {}
def create_order(self, order_id):
print(f"[Order] Creating order {order_id}...")
time.sleep(0.1)
if random.random() < 0.3: # 30% chance of failure
raise RuntimeError(f"Order {order…Browse by section
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Reliability & rate limiting — Python code examples
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